addEnum() search for attribute in parent families (closes #3642)
addEnum() search for attribute in parent families (closes #3642)

If the attribute, on which addEnum() is called, is not found in the
current family, then search for the attribute in parent families.

Also:
- Refactored global cache vars into static property.

CircleCode/dynacase-core,CircleCode/dynacase-core,CircleCode/dynacase-core