DATACMNS-596 - Polishing.

PersistentEntityInformation now falls back to null values for PersistentEntity instances that don't expose an identifier property.
DATACMNS-597 - Fixed to strict consistency check in PersistentPropertyAccessor lookup.

BasicpersistentEntity now allows subtypes to be handed into the PersistentPropertyAccessor lookup to support inheritance hierarchies as well as interface based PersistentEntity scenarios.