Added seatbelt fixedwing controller.
Flipped simple mode pitch/throttle channel input.
Fixed PID roc2Thr param names/ added them to controldemo.
Fixed a comment.
Added pressure alt measurement to kalman demo.
Merge branch 'seatbelt_controllib' of https://github.com/jgoppert/Firmware into seatbelt
Merge pull request #234 from PX4/seatbelt

Seatbelt for fixed wing