This will stop situations like we currently have where the
MANUAL_CONTROL GCS mavlink packets can still affect the vehicle
Also resolves an issue where has_new_overrides may not be set
appropriately
RC_Channel: move handling of Rover's functions into RC_Channel
RC_Channel: move auxsw handling for camera to base RC_Channel
RC_Channel: add responsibility for servorelay events
RC_Channel: move mode switch handling to base class
Peter Barker
Michael du Breuil
Andrew Tridgell