[FEATURE] PersistenceManager supports entities with composite primary keys

Its currently not possible to handle entities with composite primary keys
Please See: http://docs.doctrine-project.org/en/2.0.x/tutorials/composite-primary-keys.html

Ensures that the result of getIdentifierByObject() is reusable by getObjectByIdentifier()

Change-Id: I451b8233a69743a02d437d4374c3ae8706b65676
Releases: master
Resolves: #56601