[agl] use ground_alt from autopilot if no SRTM data available
[rotorcraft] guidance_h speed ref saturation fix

Bound ref to max accel along reference vector.
If angle can't be computed, simply set both axes to max magnitude instead of zero.

Should (tm) fix #716
[conf] sort conf example and test
[optitrack] Give feedback about following drones and fix gps
[conf] stm32-upload: only verify for dfu-util >= 0.7
Merge pull request #718 from fvantienen/optitrack_fix

[optitrack] Give feedback about following drones and fix gps
[subsystem] possibility to poweron gps and imu via gpio at init

closes #706
[airborne] check ned_initialized_f in stateIsLocalCoordinateValid
[ins] alt_float: properly reset_alt_ref if !USE_BAROMETER
[ins] ins_int: INS_SONAR_MIN_RANGE defaults to 1mm
[agl] fix waypoint edit box display and sim ground detect
[radio_control] Workaround RADIO_CONTROL_NB_CHANNELS differs in driver and radio.h

closes #700
[srtm] improving information messages about SRTM data
[simulator] pprzsim-launch: add -fg for jsbsim
[rotorcraft] gh_max_speed|accel
[conf] ardrone2_raw: remove obsolete INS_SONAR_SENS
[conf] remove old booz2_flixr airframe
[ins] remove unused/obsolete vf_int
[messages] remove some old booz messages
[dox] fix typo