[rotorcraft] CAUTION! ref_quat scaling fix

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.
[conf] rotorcrafts: update REF_OMEGA_x in examples

to half the value than before
[rotorcraft] ref_quat_int: omega, zeta accessors and settings
[rotorcraft] ref_quat_float: omega accessors and settings
[conf] settings: fix typos in stabilization_att_float_quat
Merge pull request #663 from paparazzi/ref_quat_scale

stabilization attitude: reference quaternion scale

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.