[Makefile][joystick] fix dependency and link in custom mode for ARM
add native versions of gcs/server to gitignore
[Makefile] build sim target in custom mode on ARM
[ahrs] Add Microstrain GX3 AHRS subystem

The AP stays in kill mode until it gets valid data from AHRS (using ahrs_aligner)
[ahrs] clean ahrs_gx3

- cleanup indentation, remove trailing whitespaces
- removed unused USE_GX3 flag
- move makefile to shared, as in principle it should work for fixedwings as well
- make ImuEvent a cleaner static inline function
[conf] add radio file for Turnigy 9XR from Michal
[gps_sirf] Added gps sirf
[gps] fix and cleanup sirf

Actually make it compile:
- replace cpu_time_ticks by sys_time.nb_sec_rem
- only use print function if DEBUG_SIRF

- cleanup indentation
- remove dead/commented code
- add default switch case
- some doxygen comments
Added mode dependent actuator laws
[gen_airframe] only den is negative when converting float to num/den
[toolchain] Added arm toolchain
[Makefile] slightly improve common arm makefiles
[Makefile] fix common arm toolchain stuff
[ahrs] add float multiplicative quaternion linearized Kalman Filter
[modules] digital_cam: dc_buffer is uint16, set max number as default DC_IMAGE_BUFFER
[energy_ctrl] fix dt
[energy_ctrl] output is v_ctl_pitch_setpoint, not nav-pitch anymore
[energy_ctrl] Airspeed slew always active because of defines at start. Remove confusion.
[energy_ctrl] warning if STALL_AIRSPEED not defined

Stall airspeed is automatically protected (+23%) with unexpected high airspeed when not defined... At least warn the user
[lib/ocaml] fix float conversion on ARM

On architectures/platforms where doubles need to be aligned,
link was throwing a Bus error since the floats in the received message are not aligned.
Now it just copies floats/doubles byte by byte to avoid this issue.

This should fix #421