Improve logging handler configuration
SocketDevice: Refactor server greetings to separate method
Implement loop for reading commands from Rocket
Refactor logging setup into separate method
Change tests to use same package as source

Otherwise tests can't access package-protected classes / variables.
Add possibility to listen on TrackContainer tracklist changes

By registering a new event listener on TrackContainer the observer gets
updated with data about new / deleted Tracks. This can be used to
communicate changes to Rocket, files and other destinations.