stabilization attitude: reference quaternion scale

Attitude reference quaternion:
Fix scale of angle in 2nd order model, since error quaternion contains the half-angles we get 2*omega^2*err

This means that you should halve your REF_OMEGA_[PQR] parameters to get nearly the same as before.

TODO: implement accessors to update the pre-computed values and use them in the settings handler.

Maybe we should remove the  SATURATE_SPEED_TRIM_ACCEL and the MAX_[PQR]DOT variables needed for that? Since the angle error is already bounded (and saturation in this way will make the 2nd order model non-linear...).
Would also make configuration easier if these don't need to be set...