engine failure detection
make rc loss timeout a param
flight termination mavlink outtput: limit rate
if V_RCL_LT < 0 go directly to termination
fix typo in comment
gps failure has priority over engine falure, in case both fail make sure
that the gps failure mode does not turn on the engine
Revert "datalink check: ignore onboard computer"

This reverts commit 3f8793210b47bd8e09ed2adaabc2fab966db5df6.

Conflicts:
	src/modules/commander/commander.cpp
	src/modules/commander/commander_params.c
geofence: better usefeedback if loaded
navigator: fix status information, remove fence_valid flag (this is handled by the geofence class)