PDME — Make certain ConfigurationManagement interfaces Documentable

Summary: Problem: The following ConfigurationManagement interfaces inherit
from Manageable, but do not support attached Document descriptions:
ProductClass, SpecificationCategory, Specification, ProductComponent,
ProductFunction. The descriptive string may be insufficient to
document these properly, and may be subject to controlled revision.
Therefore, these interfaces should be Documentable. The simplest
solution is to change the inheritance from Manageable to ManagedEntity.