Improvement to the code structure.
Movving mavlink code in the droidplanner project from com.MAVLink to com.droidplanner.MAVLink.
Moving all the Mavlink msg handling to a new class.
Use getters and setters in the drone class.

This way we have more control over someone changing the current drone state.
Checks when changing the state of the drone.

This is so we can start an event when something like the mode has changed.
Adds some TTS messages for interresting drone events.

Fix some part of issue #48
Merge pull request #75 from arthurbenemann/issue48

There are some big modifications to the structure on 0d7412f , so I`m pulling this to master even if it the work on #48 is not finished.