New wider interface added, several refacturings:

New wider interface added, several refacturings:
- New interface ProtocolHandler added which should be extended by listener and
  writer interfaces. Please do not implement this interface, we only use it for
  the socket registry.
- BaseListener refactured: Handling of server socket swapped out to new
  (incomplete) socket registry.
- Callback function removed from network package to save a lot (!) memory
- New network package target 'upper' added which is an alias for all upper hubs
- deliverEnqueuedPackage() basicly finished
- Some code cosmetics applied
- TODOs.txt updated