Simplify how the object actor is resolved using the actor reference

[nobeh]

Currently to achieve this is:

ActorClassType a = (ActorClassType) context().notary().get(actorReference);

This should be done much easier.

[nobeh]

Inside an actor, the following two methods are added:

• <T> T object(Reference) to resolve the actual object for a reference
• Reference reference(Object) to resolve the reference of an object