[gcs] change default maps_zoom to 20
[rotorcraft] nav approaching_time implemented

see #715
[rotorcraft] nav approaching resolution updates

The minimum horizontal distance to wp in order to mark as arrived can be changed by defining
ARRIVED_AT_WAYPOINT
which defaults to 3m.

closes #715
[fixedwing] Configurable reference generator for adaptive attitude control loop
[fixedwing] adaptive control loop telemetry message upgrade: send setpoint, reference, estimated angle and control surface setpoint for roll and pitch
[fixedwing] Corrected loiter input: cruise_throttle instead of throttle_setpoint. Added rate limiter to loiter output (pitch_trim)
[fixedwing] pitch trim rate limiter setting added
[fixedwing] adaptive: fix DT
[fixedwing] adaptive: h_ctl_ref struct
[paparazzi-center] Allow settings/modules/flightplans outside the conf directory
Merge fw stabilization adaptive updates

loiter correction and reference generator update
closes #711

* fw_stab_adapt:
  [fixedwing] adaptive: h_ctl_ref struct
  [fixedwing] adaptive: fix DT
  [fixedwing] pitch trim rate limiter setting added
  [fixedwing] Corrected loiter input: cruise_throttle instead of throttle_setpoint. Added rate limiter to loiter output (pitch_trim)
  [fixedwing] adaptive control loop telemetry message upgrade: send setpoint, reference, estimated angle and control surface setpoint for roll and pitch
  [fixedwing] Configurable reference generator for adaptive attitude control loop