IRSEPersistableReferencedObject
This is an object that can have shadow (reference) objects, which simply
point to this object, and a copy of this object's unique name or key (for storing on disk).
IRSEBasePersistableReferenceManager.isReferenced(
IRSEBasePersistableReferencedObject object)
Return true if the given referencable object is indeed referenced by a referencing object
in the current list.