implemented algorithm to calculate nutrition tables for recipes from their ingredients -> added tests.
implemented equals() method for NutritionTable -> added tests.

slight refactoring...

changed Categories to CategoryManager and added IngredientManager with respective methods (partly moved from RecipeManager to IngredientManager)

added tests to categories: they should not be created with a name that is "", null and only be created with a color code where 0 <= code <= 0xFFFFFF