Copter: skip mode change checks when disarmed

Note: there will be a follow up commit to move the checks into a
separate function so they can be called just before arming
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
Copter: land by default at end of RTL
AutoTest: remove override of RTL_ALT_FINAL parameter
Rover: fixed license text

rover is under GPL, not LGPL
AP_AHRS: fixed license text

APM is under GPL, not LGPL
AP_ADC: fixed license text

we are on GPLv3 now
PX4: Adaptations to latest build changes
PX4: Added config file fmuv2 board, not used yet
HAL_PX4: enable right FMUv2 drivers

ets_airspeed is ok, but mkblctrl driver doesn't build yet
PX4: added px4-v2 targets
PX4: added io-v2 targets
PX4: moved px4io-*.bin to ROMFS

this is more convenient than users having to copy it over
PX4: adapt rc.APM for FMUv1 and FMUv2