DroneMarker: The drone marker rotation is now done via the maps API.

There is no need for the hack I implemented some time ago because now rotation is supported by the maps api.
DroneMarker: Clean up of the DroneMarker class

Since we are using the new API to rotate the map some functions could be cleaned.
Also the dronemarker now uses the event structure of the app, so the parent fragment doesn't need to worry about it.
Merge pull request #561 from arthurbenemann/DroneMarker

Drone Marker