Basic UAVCAN support

Consider the throttle load for battery voltage calculation

Rely on theoretical value, as the closed-loop test with multimeter suggests this is the most accurate measurement

Set full voltage correctly to ensure percentage range fits. Force all users to new value by param renaming. Since this will tend to show batteries as more drained than before, this is a change in a safe direction and will not trigger unnoticed discharges.

Arming feedback

commander: Do not confuse developers with wrong comments, do not confuse users with not at all helpful "general error" messages.

position_estimator_inav: parameters descriptions added

Force failsafe