fields: Move some ForeignKeyBase to_python logic to ForeignKeyBase.get_relation_table()
fields: Move some ForeignKeyBase to_python logic to ForeignKeyBase.get_relation_table()

jleclanche/pywow,jleclanche/pywow,jleclanche/pywow,jleclanche/pywow,jleclanche/pywow,jleclanche/pywow