FIELD OF THE INVENTION The present invention relates to skin care agents and cosmetic skin lightening compositions and, in particular, selective dihydrochalcone derivatives as skin care/ lightening agents and cosmetic and/ or dermopharmaceutical compositions containing the same. The invention is directed to cosmetic compositions comprising dihydrochalcone derivatives in effective amounts in the said compositions alongwith cosmetically and/ or dermopharmaceutically accepted vehicles with or without other skin benefit agents. The invention is specifically further directed in providing dendrite elongation inhibitory compositions involving the said dihydrochalcone derivatives. BACKGROUND AND PRIOR ART An increase in skin pigmentation over the basal constitutive level is referred to as facultative pigmentation. A major stimulus of facultative pigmentation in humans is UV radiation. UV radiation induced skin pigmentation or tanning as it is commonly known, involves several processes like increased proliferation, enhanced tyrosinase expression, increased dendricity and increased transfer of melanin to ease the transfer of the melanin keratinocytes. Skin lightening is an important contributor to skin care attribute of cosmetic preparation/ compositions, especially among darker skinned people including Asian population. Such a need includes a lightening of basal skin tone. Also it is desired by persons having spots, freckles or lesions which are hyperpigmented and thus need to be diminished. In some other situations, subjects may desire to reduce their natural skin colour or the skin darkening caused by exposure to intense sun rays. The degree of pigmentation of the skin is thus a principal cause of concern for many people. The complexion of the skin is determined by the pigment melanin. Melanocytes are the pigment producing cells that provide photo protection to the skin by synthesizing and distributing the pigment melanin to keratinocytes. These melanocytes are located in the basal layer of keratinocytes. Melanocytes and keratinocytes are resident population of epidermis and the color of skin is only because of the melanin in keratinocytes which is transferred from melanocytes. Melanocytes are derived from neural crest cells, comprise of 1-2% of epidermal cell population and are solely responsible for the production and transfer of melanin to keratinocytes and pilosebaceous follicle. Melanin is synthesized and packed in cytoplasmic organelles of melanocytes, called melanosomes and are later transferred to keratinocytes through specialized structures in the melanocytes called dendrites. Since melanocytes are the minor population in the epidermis, the presence of the multiple dendrites facilitates transfer of melanosomes to keratinocytes that surround melanocytes. Movement of the melanosomes along melanocyte dendrites is also necessary for the transfer of melanin pigment from melanolcytes to basal and suprabasal keratinocytes to maintain the normal skin color. Melanocyte dendrite formation is regulated by multiple signaling pathways stimulated by paracrine factors released by keratinocytes as reported by J. Hara et. al. in Invest. Dermatol., 2000, 114, 438-443. The dendricity of melanocytes is regulated by various intrinsic and extrinsic factors. Addition of agents that increase the intracellular levels of cyclic adenosine monophosphate, dibutyryl cyclinc adenosine monophosphate or isobutylmethyl xanthine (IBMX), all of which has strong effects on dendrite formation (Glynis et. al., J. Invest. Dermatol., 2007, 127, 668-675). Each melanocyte makes contact with around 30-40 keratinocytes and this constitutes the epidermal melanin unit. Mammalian melanocytes in the epidermal unit extend their dendrites towards keratinocytes in response to UV rays in addition to proliferation and melanin synthesis leading to tanned skin (Suzuki et al.. In Vitro Cell Dev. Biol. Anim., 1993, 29, 419-426). Also, increased number of dendrites and increase in the length of dendrites, higher levels of transfer of melanin to keratinocytes is an established phenomenon while subjected to the UV rays. Thus skin colour can be determined/ regulated by modulating the elongation of dendrites or dendrite numbers (Akihiro, Fragr J, 2005, 33, 30 and Tada et. al.. Bio. Ind., 2005, 22, 12-17). Under normal conditions it is not the number of melanocytes in the skin that determines the degree of pigmentation but their levels of activity and the transfer of melanin in to the neighboring keratinocytes is the important factor. Phospholipse A2 secreted by kertinocytes is also known to mediate melanocyte dendricity. The effective transfer of the synthesized melanin by the melanocytes to the keratinocytes plays a very critical role in the skin colour than the extent of synthesis of melanin by the melanocytes. The most effective mode of transfer of the melanin to the keratinocytes is governed by the dendritic phenomena of the melanocytes. Abrogating the dendriticity of melanocytes is of great importance for controlling skin colour (Yuko et. al., Biochimica et Biophysica Acta, 2006, 1769, 487). There are several dendrite inhibitors already reported in the literature. Benzoquinone group of chemicals that includes methyl ophiopogonanone B and centaureidin, benzopyranone, xanthanone derivatives were reported to inhibit dendrite formation in melanocytes and effectively affect the skin colour (Yuko et. al., Biochimica et Biophysica Acta, 2006, 1769, 487). Inhibiting the dendrite formation in melanocytes is thought to be more effective in the related prior arts than tyrosinase inhibition for the purpose of skin lightening/ whitening cosmetics (Tada et. al., USP: 7, 141, 601, 2006). US patent 7141601 and Korean patent 20050084088 A by Tada et al. are directed to a method of inhibiting the elongation of melanocytic dendrites through a skin preparation comprising of methylophiopogonanone B (2, 3-dihydro-3[(4-methoxyphenyl) methyl]-5, 7-dihydroxy-6, 8-dimethyl-4H-l-benzopyran-4-one) extracted from the tubers of Ophiopogon japonicus ker-Gawler. JP 2004143073 A further illustrates a 1, 3-dioxolane derivative of methyl¬ophiopogonanone B to possess the same property of inhibiting the elongation of melanocytic dendrites. JP 2001335420 A is related to a skin lotion comprising the essence of rhizomes of Acorus calamus; JP 2001335421 A is directed to the essence of Sophora subprostata; JP 2003081748 A teaches a fruit essence of Forsythia suspensa Thunb. Vahl of Oleaceae; JP 2003081747 A illustrates a skin care preparation comprising the essence of Lonicera japonica Thunb preferably the essence of bulbs, leaves and stems; JP 2002053421 A is directed to a cosmetic skin care preparation comprising Maackiain derived form the rhizomes of Sophora subprostrata; JP 2002154919 A comprises of a skin care preparation comprising the essence of the fruit of Phaseolus radiatus L.; JP 2003081807 A is related to a bleaching cosmetic comprising an essence of Calendula officinalis L. and preferably an essence of a flower bud, a leaf and a stem; JP 2003113027 (A) is directed to a bleaching cosmetics by incorporating the essence of preferably enlarged root of plant of genus Ophiopogon such as Ophiopogon japonicus ker-Gawler etc.; JP 2003252742 A discloses a skin preparation having high bleaching effect comprising yeast extract as the active ingredient; JP 2001335502 A is related to a skin care preparation comprising the essence of rhizomes of Nardostachys jatamansi; JP 2002020303 A illustrates a cosmetic skin care preparation comprising the essence of rhizome of Thalictrum minus var. hypoleucum; JP 2004250354 A is related to a cosmetic preparation comprising extract of a plant belonging to Achillea family; JP 2003081746 A is directed to a bleaching cosmetics comprising an essence of Uncaria gambtiir ROXBURGH, preferably the essence of leaves and sprigs; JP 2002154920 A is directed to a cosmetic skin care preparation including the essence of a ripe dried seed, preferably a fruit of Prunus armeniaca L. var. ansu axim. of the family Rosaceae; JP 2001335485 A directed to a skin care preparation comprising of a berberine derivative; all of which have the dendrite inhibition property. However, some of these products are associated with simultaneous disadvantages associated with each of them. For example, Acorus calamus is considered to be cytotoxic as reported by Padmaja et al. in Fitoterapia. 2002, 73, 508-510. EP 1570838 Al is mainly directed to dendrite elongation inhibitor for melanocytes comprising of centaureidin that was used directly or in the form of a physiologically acceptable salt in cosmetic skin preparations intended for alleviating dyschromatosis to which the amount of melanin produced less contributes resulting form the accelerated migration of melanin granules from melanocytic dendrites. While inhibiting the elongation of dendrites that occurs when melanocytes allow melanin granules to migrate is a well known skin lightening mechanism not so many lightening agents utilizing such a mechanism are known in the art and it can thus be said that there is a strong need in the art for the development of new skin lightening agents utilizing such a mechanism. Therefore, the existing state of the art clearly reveals the need for newer, effective and safe dendrite elongation inhibitors and more importantly the need for possible isolation of the said dendrite elongation inhibitors from renewable resource materials such as plants. OBJECTS OF THE INVENTION It is thus the basic object of the present invention to provide for a new sl