Add ModelWithFieldAttributes *before* PolyModel, so that everything does not become a "ModelWithFieldAttributes" in the Datastore. The way PolyModel works, each Model class hierarchy is stored in the Datastore as the class that directly inherited from PolyModel. So, we do not want to insert ModelWithFieldAttributes *after* PolyModel by inheriting *from* PolyModel, or everything would just be a ModelWithFieldAttributes in the Datastore, instead of Person, Work, Group, etc.