AP_Math: added wrap_360_cd() and wrap_180_cd()

moved from per-vehicle code
Plane: removed old angle wrap code
Rover: use new angle wrap code
Copter: use common angle wrap code
AP_AHRS: prevents compass flyaways for plane and rover

this switches to the GPS for yaw if the compass has dragged us off by
more than 45 degrees from the GPS heading, and the wind speed is less
than 80% of the ground speed.
Plane: report compass health in SYS_STATUS