HBX-1225 Proxy class should be used for referring many-to-one property declaration in generated class

Many-to-one property referencing a PersistentClass should be its proxy, if it has one, as Hibernate will attempt to set the property with an instance of the proxy, that is not an instance of the property's concrete type.
HBX-1225 Test case to demonstrate failure case and correction, and fixes to test cases demonstrating the corrected generation works