DESCRIPTION PRECOATED SHEET HAVING GOOD WORKABILITY AND SCRATCH RESISTANCE AND METHOD FOR PRODUCTION THEREOF TECHNICAL FIELD The present invention relates to precoated sheets excellent in workability and scratch resistance. The precoated sheet of the present invention has a coated film with an appearance of an orange peel surface exhibiting waviness of a relief shape and has the excellent characteristics of resistance to sticking of dirt even if dirt deposits on it and muting of any scratches on the surface. Further, the present invention relates to a method of production of a precoated sheet enabling the easy formation of an orange peel-like relief appearance by the multilayer simultaneous coating method. The "precoated sheet" referred to here is defined as a sheet material comprised of a substrate on at least one surface of which a coated film is formed. As the substrate, it is possible to use, in addition to a metal, paper, wood, plywood, etc., a resin sheet of polypropylene (PP), polyethylene terephthalate (PET), etc. BACKGROUND ART One typical example of a precoated sheet, precoated metal sheet, is being used in a broad range of applications from buildings, ships, bridges, and other large structures to various machinery, automobiles, furniture, electrical appliances, and other smaller objects and daily necessities. In general, these metal sheets are coated by so-called "post-coating" after being worked and assembled. With post-coating, since the coated object is three-dimensional in shape, spray coating of solvent-based coatings, electrostatic coating of powder coatings, and other noncontact type coating methods have been used. In the fields of housings of home electrical appliances and office automation equipment, roofs and walls, indoor walls, and other building materials, sundry goods, auto parts and their housings, etc., orange peel-like coated film appearances helping to mask surface defects are being sought. With spray coating, electrostatic coating of powder coatings, and other non-contact coating methods, the insufficient leveling of the coatings have facilitated the formation of a distinctive orange peel appearance at the coated surface and have enabled the easy formation of an orange peel surface. Recently, in the fields of building materials, home electric appliances, sundry goods, automobiles, etc., the conventional post-coating method of shaping and assembling the metal sheets, then coating them has often been replaced by the precoating method of shaping metal sheet coated in advance (precoated metal sheet, abbreviated as "PCM"), then joining it to form products. Introduction of the precoating method has the merits of enabling elimination of the coating process at the demand side, solving the problems of pollution and environmental contamination due to disposal of waste products of coatings, and enabling the work space previously used for coating to be converted to other applications. However, in particular in the field of precoated steel sheet, workability is strongly required as one of the product characteristics, so introduction of orange peel surface coated film with a solid, thick appearance has not been easy. The conventional methods of formation of coated film with an orange peel appearance include (1) the method of using a coating containing resin beads, (2) the method of using a coating containing inorganic beads, (3) the method of utilizing printing, (4) the method of using mesh rolls, (5) the method of using electrostatic powder coating, etc. For example, JP 4-370164 A describes a method of using a coating composition containing thermoplastic resin powder of an average particle size of 10 to 50 µm to obtain an orange peel surface appearance coated film (resin bead method). The method of JP 4-370164 A defines the difference in solubility parameter with the vehicle resin and defines the solution viscosity of the resin powder at the coated film baking temperature. Further, it describes that in a coated film obtained by coating and baking a coating composition on a coated object, in cross-section, the resin powder melts and flattens to a certain extent and the vehicle resin cures above it to form a film and that in such an obtained orange peel surface coated film, the height of the projecting parts measured from the lowest coated film surface is 2 to 50 jam or so and the width of one projecting part (size indicating spread of projecting part) becomes 1 to 10 mm or so. JP 11-104557 A also describes a resin bead method. This method coats and bakes a coating composition containing a thermosetting resin, an amino resin with a lower surface free energy than the thermosetting resin, and resin beads which melt at the time of baking of the coated film and which do not dissolve in the coating. JP 5-32918 A describes an inorganic bead method. This method uses a coating composition containing glass beads of sizes of less than 0.3 mm and a colored aggregate of 150 to 200 mesh in a specific ratio. JP 6-206047 A describes a printing method partially forming three-dimensional patterns of a coated film thickness of at least 2 µm or more by printing, then forming a topcoat layer over the entire surface. JP 2002-361164 A discloses a mesh roll method of coating a coating comprised of a coating resin (base resin) to which an additive having a distinct solubility parameter is added using mesh rolls so that the additive with poor compatibility with the base resin separates in the film-forming process to form a cissing-like fancy appearance. The conventional method of using a coated film containing resin beads has the problems that the reproducibility of the patterns in the heating process is not necessarily good, it is difficult to finely adjust the thickness by the heating pattern, the coating stability is poor, and cleaning becomes necessary when changing the coatings (poor coating due to the beads occurring). The method of using an inorganic bead-containing coating to form the orange peel surface has the problems of a larger amount of beads exposed at the surface of the coated film, deterioration of the coated film due to detachment of the beads, and poor workability of the coated film. Further, there is also the problem that it is difficult to stably suspend solid beads in a coating. Further, there is the difficulty that the surface of the coated film is left with a rough feeling. In the printing method, basically the three-dimensional patterns are printed, then dried by heating, then the topcoat layer is formed and dried by heating again in a "two-coat two-bake method". For this reason, the coating process becomes troublesome and the cost rises. In the case of the mesh roll method, it is difficult to adjust the thickness to a uniform one and therefore some thin parts are caused, so the precoated metal sheet has problems in corrosion resistance. In the electrostatic powder coating method, the line speed is a small 10 to 20 m/min, so the productivity is low and the cost ends up becoming high. DISCLOSURE OF THE INVENTION An object of the present invention is to provide a precoated metal sheet and other precoated sheet having an orange peel like coated appearance and excellent in workability and scratch resistance and a simple method of production of such a precoated sheet. The inventors took note of the phenomenon that a multicoated film layer obtained by stacking layers formed from coatings of different properties is disturbed in the interface layers of the multicoated film at the time of drying by heating resulting in an uneven flow of the coating. Further, the inventors discovered that while this uneven flow is a fine convection phenomenon in the coated film, it induces large changes in the relief shapes on the level of several millimeter on the outermost surface of the coated film. The inventors engaged in intensive research and succeeded in forming orange peel-like smooth relief shapes on the surface of a coated film by optimizing the surface tensions of the coatings forming the different layers and the heating conditions of the coated film and thereby completed the present invention. The precoated sheet according to the present invention has a coated film with an outermost coated film layer of an orange peel appearance and with an interface between the outermost coated film layer and its lower coated film layer of a substantially or completely continuous wave structure, that is, the interface formed a substantially or completely continuous wave structure surface, neither the lower coated film layer nor the outermost coated film layer has any discontinuous parts, and the entire surface of the substrate is substantially covered by these, so the precoated sheet is also excellent in workability and scratch resistance. The present invention has as its gist the following: (1) A precoated sheet excellent in workability and scratch resistance characterized by having a coated film with an outermost surface having a filtered centerline waviness curve (Wca) of 0.35 µm