[ahrs] int_cmpl_quat: scale the correction in update_accel with AHRS_CORRECT_FREQUENCY
Allow tuning of the rate and bias gains.
Scaling correction by AHRS_CORRECT_FREQUENCY should also give you
roughly correct tuning for 100Hz fixedwings, see #240.
[ahrs] int_cmpl_quat: lower correction from accel update
double gain scale to allow for a nicer range of the gains
[ahrs] int_cmpl_quat: some more adjustable correction gains
not tested in flight yet...
[ahrs] int_cmpl_quat: use signed integers for correction scaling
beware of the usual arithmetic conversions!!