Deleted RestrictedGeneralizedMorphismCategory

and installed new IsWellDefined method for GeneralizedMorphisms
Deleted ToDo-management from GeneralizedMorphismCategory
IdentityMorphism in GeneralizedMorphismCategory
Renamed: AssociatedMorphism -> MorphismAid

because the associated morphism is part of the triple
(domain, associated morphism, codomain)
and not part of the triple
(source aid, morphism aid, range aid).
GeneralizedMorphismFromFactorToSubObject

now based on ImageEmbedding and CoastrictionToImage
instead of MonoEpiFactorization