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
  
Any idea for how to handle permanently failed messages? Is there even a reason to fail them permanently? Why not just keep retrying until they succeeded?