Automated event handler invocation after successful event persistence

[krasserm]

At the moment, a persist handler must explicitly call onEvent for successfully persisted events:

persist(evt) {
  case Success(_) =>
    onEvent(evt)
    // ...
  case Failure(e) =>
    // ...
}

This should be automated so that application code doesn't need to call onEvent anymore:

persist(evt) {
  case Success(_) =>
    // ...
  case Failure(e) =>
    // ...
}

[krasserm]

Also covered by this ticket is a new recommendation how to define command, event and snapshot handlers:

• Instead of override val onCommand: Receive = { ... } a command handler should now be defined as override def onCommand = { ... }
• Instead of override val onEvent: Receive = { ... } an event handler should now be defined as override def onCommand = { ... }
• Instead of override val onSnapshot: Receive = { ... } a snapshot handler should now be defined as override def onSnapshot = { ... }