Turned all control outputs into NED frame moments

This is validated in real flight with a correct mixer setup. The rationale behind this change is: In PX4 all control inputs for all vehicles types are expressed as body angular moments, consequently a manual input of negative pitch should make the plane pitch down (and the quad pitch down). The provided mixers are set up to behave accordingly. Consequently all controllers have to stick to the same convention, even though signs in "classic" fixed wing controller outputs may behave differently.