Changes to Marshalling/Added LoadoutModel/Cleaning up of namespace WastelandA23.Persistence

-Some restructuring of marshallers class hierarchy
-Handling of types with attribute DerivedType improved: Now works for derived types for marked base types
-AssignableItems in Loadout no longer List<string> but List<AssignableItem>
-Cleaned up all classes in namespace WastelandA23.Persistence with CodeMaid
-Added Project(ClassLibrary) WastelandA23.Model with a first database model created with EF6