HIL and fixed wing fixes - gives perfect results in simulation

@thomasgubler Please review for fixed wing changes. @DrTon @julianoes Please review for state machine changes.

This change addresses the following challenges / issues:

  * HIL required a RC previously and also the power module to be connected. Fixed.
  * The HIL voltage was fighting with power module readings. Fixed.
  * Mode switching from QGC completely supported
  * Remains on the restart-mission-from-start feature used previously confused the navigation engine on the first waypoint. Fixed now (found during test flights two weeks ago)
  * Added default gains for a number of fixed wing airframes. Will need more tuning, but should be reasonable.
  * The waypoint switching / reached distance now depends on the L1 distance and airspeed. This makes much smoother transitions.

This has been tested extensively in HIL and should be good to merge. Test flights (in particular on multicopter) would be appreciated.