1. A cosmetic self-tanning agent with a sunscreen effect based on dihydroxyacetone, comprising the following ingredients, based on the total weight of the emulsion: (a) 7 to 18.5 percent by weight of a mixture of the UV filters octyl salicylate, octyl methoxycinnamate and benzophenone-3 in a ratio of 1.0-2.0:0.8-2.5:0.8-2.0; (b) dihydroxyacetone (DHA) in a liposomal transport system consisting of DHA and phospholipids with a DHA content of 0.5 to 5 percent by weight, where the amount of liposomal solution is in the range of 1.5 to 25 percent by weight, plus also unencapsulated DHA in an amount of 1 to 4 percent by weight, each based on the total weight of the mixture; (c) an antioxidant selected from the group consisting of tocopherol, ascorbic acid, calendula extract and a mixture thereof, in an amount of 0.01 to 5.0 percent by weight of the total mixture; (d) a moisturizer selected from the group consisting of aloe vera, phospholipids, phospholipid mixtures, sodium hyaluronate, glycerol and mixtures thereof, in an amount of 0.1 to 16 percent by weight of the total mixture; and cosmetic vehicles and additives. 2. A cosmetic agent according to claim 1, wherein the total amount of the UV filters (a) is in the range of 10 to 16 percent by weight. 3. A cosmetic agent according to claim 1, wherein the amount of DHA (b) is in the range of 0.8 to 1.8 percent by weight, where the amount of the liposomal solution is in the range of 1.5 to 10.0 percent by weight. 4. A cosmetic agent according to claim 1, wherein the amount of antioxidants (c) is in the range of 0.01 to 0.5 percent by weight. 5. A cosmetic agent according to claim 1, wherein the amount of moisturizers (d) is in the range of 0.7 to 5 percent by weight. 6. A cosmetic agent according to one of claims 1 through 5, wherein it contains the following ingredients to achieve a light golden color: (a) the mixture of octyl salicylate, octyl methoxycinnamate and benzophenone-3 in a ratio of 1.0-2.0:0.8-2.5:0.8-2.0, with the amount of each individual UV filter being in the range of 3 to 7.5 percent by weight; (b) DHA in a liposomal carrier system with a DHA content of 0.5 to 1.0 percent by weight, plus unencapsulated DHA in an amount of 1.4 to 2.6 percent by weight; (c) an antioxidant mixture of tocopherol, ascorbic acid and calendula extract in an amount of 0.15 to 0.25 percent by weight; (d) a moisturizer mixture with glycerol in an amount of 2.5 to 4 percent by weight; plus other cosmetic vehicles and additives. 7. A cosmetic agent according to one of claims 1 through 5, wherein it contains the following ingredients to achieve a medium to dark bronze color: (a) the mixture of octyl salicylate, octyl methoxycinnamate and benzophenone-3 in a ratio of 1.0-2.0:0.8-2.5:0.8-2.0, where the amount of each individual UV filter is in the range of 3 to 7.5 percent by weight; (b) DHA in a liposomal carrier system with a DHA content of 1.3 to 1.7 percent by weight, plus unencapsulated DHA in an amount of 2.7 to 3.8 percent by weight; (c) an antioxidant mixture of tocopherol, ascorbic acid and calendula extract in an amount of 0.15 to 0.25 percent by weight; (d) a moisturizer mixture with glycerol in an amount of 2.7 to 4 percent by weight; and other cosmetic vehicles and additives. 8. A cosmetic agent according to one of claims 1 through 5, wherein it contains the following ingredients to achieve a medium to dark rosy bronze color: (a) the mixture of octyl salicylate, octyl methoxycinnamate and benzophenone-3 in a ratio of 1.0-2.0:0.8- 2.5:0.8-2.0, where the amount of each individual UV filter is in the range of 3 to 7.5 percent by weight; (b) DHA in a liposomal carrier system with a DHA content of 1.2 to 1.6 percent by weight, plus additional unencapsulated DHA in an amount of 2.9 to 4.0 percent by weight; (c) an antioxidant mixture of tocopherol, ascorbic acid and calendula extract in an amount of 0.02 to 0.04 percent by weight; (d) a moisturizer mixture in an amount of 0.7 to 1.1 percent by weight; plus other cosmetic vehicles and additives. 9. An agent according to one of claims 1, 6, 7 or 8, wherein the UV filters (a) comprise a mixture of octyl salicylate, octyl methoxycinnamate and benzophenone-3 in a ratio of 1:2:1.