Refactored getInheritings

Added RollbackCatcher to Cache::AbstractTest

Removed the override of getInheritings(T origin, int level) method in
impl.GenericService class.

Bug fix in ExtendedSignature.init. initialize supers before calling
super.init().

We use isSpecializationOf in method isAttributeOf.

Simplification in CompositeInheritanceService::baseSupersStream end
addition of a related unit test
test006_getInheritings_VertexAndItsSuperHaveNotSameMeta.