=doc 3764 revise recommended practice for Props creation

- it is not recommended to use Props.apply(=> Actor) within an Actor
- it is recommended to use that method in the Props factory method in
  an actor’s companion object
!act,doc,rem,tes 3823 remove deprecated Props methods

- rewrite deprecated usages to their recommended counterparts
- TestActorRef now verifies mailbox requirements
- CallingThreadMailbox now exposes proper messageQueue type for
  inspection
Merge pull request #1933 from akka/wip-3764-props-docs-∂π

clean up docs and deprecation around how to create Props