+per #15229 defer for PersistentActor

* Deferred events are not persisted, thus will not participate in replays
  etc. If users want events to be persisted, they can simply use
  `persistAsync` instead.
* This rewrite relies on the Journals' Resequencer
  to return the messages in the expected sequence.
* Includes docs updates for java/scala/java8

Resolves #15229
Depends on #15227