[radio_control] spektrum for nps/sim

Ocaml sim always uses the radio.xml file and sends ppm values in usec.
So for the time beeing you need to use the spektrum.xml radio file for the sim target if you really want to use the RC in the simple OCaml sim.

closes #503
[conf] update examples using spektrum for sim
Merge pull request #851 from paparazzi/spektrum_sim

[radio_control] spektrum for nps/sim

OCaml sim always uses the radio.xml file and sends ppm values in usec.
So for the time beeing you need to use the spektrum.xml radio file for the sim target if you really want to use the RC in the simple OCaml sim.

closes #503
[generators] add type bool for gen_settings
[rotorcraft] only go to HOME mode if in NAV

then you don't have this "failsafe" in manual modes anymore,
but it will prevent issues like #850
[gen_settings] fix bug when target is not specified (use default list)
[gen_settings] only check targets on makefile nodes
[radio control] spektrum also usable for intermcu
[ins] hack float_invariant to support geo_mag module

closes #858 until we have a proper solution of publishing local magnetic field via ABI messages
[ardrone2] add rm_dir command
[ardrone2] send filter status from navboard

- it allows to see if the mag is crashed or not
- set a max retry on the reset PIC board hack (which doesn't seems to
  help anyway)
[module] add agl_dist module
[math] fix polyfit init
[airframes] fix quad_navgo actuators for nps
New joystick file for RC trainer
[modules] Added temperature adc module

Added temperature driver for analog sensors (LM35 and 100k NTC)

closes #857
[modules] add airspeed_ms45xx_i2c module

- differential pressure is filtered with a butterworth lowpass
- including (persistent) settings for pressure scale and offset
- add AIRSPEED_MS45XX message

closes #852
[nav] takeoff detection module

set the launch variable to true based on pitch angle
[ocaml] support display of formatted string in messages

this should close #796
to display an integer (or array of integer) in HEX, just add format="%x" to the field in messages.xml
[modules] separate USE_AIRSPEED_xx flags