Add better support for connecting actors to each other

[TylerBloom]

Currently, if one actor needs to have a handle to another actor, it must explicitly declare that in its state. This can make constructing a series of interconnected actors tricky. It also can distract from the core logic of an actor. One possible solution is for the actor builder to keep a tuple of different clients (or tuple of containers of clients) that is then passed to the scheduler.