Rover: support new RADIO_STATUS msg
Copter: support new RADIO_STATUS msg
Plane: support new RADIO_STATUS msg
Copter: split up loiter into 4 steps

Reduces disruption to the main loop but also introduces a delay of 30ms
to navigation output
Copter: allow override of auto throttle mode
Copter: update Y6 defaults
Copter: Corrected SR0 & SR3 parameter descriptions
Merge remote-tracking branch 'upstream/master'