remove the Actor trait

- Props are created just from a Behavior factory
- added Static behavior for when no change is needed
- add a sample demonstrating the use of vars
break out akka.typed into its own project
add first test cases
added Pure style and tests

- everything in Pure is completely pure, see PureSpec on how that looks
- added EffectfulActorContext for testing all kinds of Behaviors, see
  BehaviorSpec for how that feels