ElementModel factory, CommonObject class

OK, the create method for model elements now models the create element for Rolonic Elements, which is goodness. Indeed, if you now look at the check register you will see that we are able to use the same model class, ActionModel, to model two different Rolonic Elements. And we are ready for DRM binding, only that project will be delayed a bit...

I'll note that as the DRM matures we are having more and more duplicate code. And while the JTransaction interprets the DU of the Transaction Rolon, when we implement the equivalent capability for Query we will need instead to interpret a model DU instead. Not good. So it is time to create a CommonObject class which will be the base class for both PersistentObject and ElementModel. And that should keep me busy for a while. Hopefully the result will make COODBMS a lot easier to learn, though it means a lot of changes to CowDb.