someone should look at remoting vs. timeout (i.e. which is sent around),
because I removed that in some places. It might simply be irrelevant
once we remove the Future special-casing.
- removed SelfActorRef
- added an ActorContext interface that provides a view into ActorInstance
- the ActorInstance (as ActorContext) gets injected into the Actor
- moved self methods like sender and reply directly to the Actor
