+per #15279 FSM for PersistentActor

Located in akka-persistence because persistence is experimental and probably should not be used in akka-actor
By stop I mean the logical FSM stop, when the FSM reaches it's final step. Logically this means that some process, handled by the FSM, has ended, so, if someone tries to start FSM with the same persistence ID after it has been stopped it's useful to prevent it, in case you don't want the same process to be restarted.
I've left an option to override it in case a stopped FSM should be restarted in initial State.

In case of the regular Akka actor stop the last saved state is considered the current state.