Feature/notifications

- Refactored NotifierManager-EmailActor-EmailExecutorActor interplay
- All HerculesActor now have a member value 'notice' which is a NotifierManager. 
- The NotifierManager has four methods: info, progress, warning, critical and calling each method sends a message to the corresponding "channel"
- Which channel(s) each notification type listens to is configured in application.conf
  
Do we really want to start up a system by default here? Since it's a expensive operation, and most of the time we will want to pass the system for the notifier from the "host system", and only create a separate system for this in tests, I think maybe it's better not to have it as default.