Fix errors baking tree models.

When generating code for tree models, bake incorrectly assumed that the parent/child associations had separate tables. Reloading the registry by itself should work, however, composer caches that files do not exist and requires us to manually include the newly generated class.

I also fixed another error where generating views for tables with no primary key would issue notices and generate incorrect code. Since bake can't really do much with tables that don't have primary keys I think it is best for now to error out.

Refs #4914