On the state of StateTree and the emergence of ActorID's

- Why are there **two** maps on the `StateTree`?
- Why is the actor state map `Address -> ActorState` instead of `ActorID -> ActorState`

```go
// current StateTree on the spec
type StateTree struct {
SystemActors {ActorName: addr.Address}
ActorStates {addr.Address: actor.ActorState}
}
```

```go
// proposed
type StateTree struct {
ActorStates {actor.ActorID: actor.ActorState}
}
```