AP_NavEKF: Improved magnetometer consistency checks

A magnetometer axis that fails the innovation consistency check will cause
all axes not to be used. If this condition continues for 10 seconds, a
magnetometer timeout condition will be declared. When the timeout has
occurred, if it is not a fly forward vehicle, then individual channels
will be used again, but with a reduced weighting.
AP_AHRS: added vehicle class to AHRS

used by EKF to control use of get_fly_forward()
AP_NavEKF: cleanup some build warnings

Pair-Programmed-With: Paul Riseborough <p_riseborough@live.com.au>
AP_NavEKF: use AHRS vehicle class for sideslip calculation

Pair-Programmed-With: Paul Riseborough <p_riseborough@live.com.au>
Plane: set AHRS vehicle class
VARTest: fixed build
Replay: added vehicle class detection
Rover: set AHRS vehicle class
Copter: set AHRS vehicle class