[fixedwing] stabilization adaptive: loiter correction and reference generator update

- Loiter correction: loiter function inputs throttle preset and outputs pitch offset (pitch_trim) to the pitch loop setpoint. The throttle preset has to be v_ctl_auto_cruise_setpoint (set by the user via gcs), not v_ctl_throttle_setpoint (set by vertical guidance loop), otherwise pitch_trim is affected by vertical control. Pitch is already set in vertical control, so there is no need to correct it with loiter function. 
Rate limiter also added to pitch_trim.
- Reference generator update: - added possibility to configure reference generator in airframe file.  The damping and cut-off frequency can be different for roll and pitch. Telemetry message "H_CTL_A" updated with setpoint, reference, estimated angle and control surface order.