When creating a UDF, the Invocation class and method should be optional

According to Teiid Developer Guide, the Invocation Class and Method are optional properties, because in the cases where the function is REQUIRED to be a push down, it will never be called by the engine.

Also, it would be nice for the Category, to present the list of current categories that have been defined just so you can select an already defined one (this just keeps user typing errors to minimal) or let the user override and add a new one if one if needed.