Port AObservableObject bool cast operator to an AObject class

Currently the null cast is on the AObservableObject class, but bundling it together with the baggage of observably is unnecessary.

1. Create a new abstract class AObject.
2. Port the operator to the new class.
3. Have AObservableObject inherit from AObject.

This could be considered a breaking change from a strict standpoint, so that should be taken into consideration before the change is committed.