Feature/packager plugin

This PR includes a ugly merge conflict resolution, due to me forgetting to rebasing my feature branch before  pushing. But I hope it can still be accepted. :wink: 

As for what's in here (copied from relevant commit):

This includes setting up a simple logger which will write under /var/log/hercules.log at the moment. Later we might want to hook this up to logstash or at least make it a rotating log.

I also configured the app main entry to by default try to get the roles which it should start up (master, watcher, ...) from the application.conf. That way one or more roles that we want running on the same machine can be started up together.

Also changed a returns -> return in the documentation (because that is the correct tag to use).