[rotorcraft] force MODE_STARTUP instead of KILL until ahrs is aligned

- Go to MODE_STARTUP (which defaults to AP_MODE_KILL) instead of AP_MODE_KILL as long as the ahrs is not aligned.
- Remove AUTOPILOT_DISABLE_AHRS_KILL from all example airframes (but kept the functionality for now).

MODE_STARTUP is set to AP_MODE_NAV for the autonomous (without RC) ARDrone2.
Without AUTOPILOT_DISABLE_AHRS_KILL it will force MODE_STARTUP until the ahrs is aligned,
but still not allow to turn on the motors (as that also checks for ahrs_is_aligned).

As far as I can see this should solve #964 as long as you don't have AUTOPILOT_DISABLE_AHRS_KILL defined.
[rotorcraft] arming: only check if motors can be armed if ahrs_is_aligned
[sim] remove launchsitl symlink

Please use pprzsim-launch directly, the launchsitl symlink was only meant to provide (partial) backwards compatibility for some time.
closes #919
[modules] rename flight_time to time_countdown

closes #886
[messages] possibility to add descriptions
Merge pull request #983 from paparazzi/ahrs_kill

[rotorcraft] force MODE_STARTUP instead of KILL until ahrs is aligned

- Go to MODE_STARTUP (which defaults to AP_MODE_KILL) instead of AP_MODE_KILL as long as the ahrs is not aligned.
- Remove AUTOPILOT_DISABLE_AHRS_KILL from all example airframes (but kept the functionality for now).

MODE_STARTUP is set to AP_MODE_NAV for the autonomous (without RC) ARDrone2.
Without AUTOPILOT_DISABLE_AHRS_KILL it will force MODE_STARTUP until the ahrs is aligned,
but still not allow to turn on the motors (as that also checks for ahrs_is_aligned).

This closes #964 (as long as you don't have AUTOPILOT_DISABLE_AHRS_KILL defined).
[build] don't compile natnet if not needed
[modules][messages] mission: LLA waypoints in 1e7deg instead of float

A 32bit float has 23bits for the mantissa, which is a bit more than 7 digits.
Since you already use 3 digits to represent the part to the left of the decimal point, that leaves about 4 digits for the rest..
So in the worst case of 180deg you have a resolution of only ~3m!

With 1e7deg 32bit int you get ~1cm resolution.

addresses first part of #984 (at least for the rotorcraft version, fixedwing version still converts to LLA float in between...)
[modules] mission_rotorcraft: only check for ned_initialized_i
Merge pull request #986 from paparazzi/mission_module_latlon_int

[modules][messages] mission: LLA waypoints in 1e7deg instead of float

A 32bit float has 23bits for the mantissa, which is a bit more than 7 digits.
Since you already use 3 digits to represent the part to the left of the decimal point, that leaves about 4 digits for the rest..
So in the worst case of 180deg you have a resolution of only ~3m!

With 1e7deg 32bit int you get ~1cm resolution.

In the fixedwing version LLA is still converted to float first, since we seem to miss functions to convert LLA to UTM in int or double...
At least it is better for rotorcraft and same as before for fixedwings...
[messages] remove description node again for now

seems server/GCS (OCaml lib) can't handle it, as they fail with
Fatal error: exception ExtXml.Error("Error: Attribute 'type' expected in <<>>")
[submodules] updated to a new chibios repository
[ocaml] filter for 'field' tag when looking at messages
Merge remote-tracking branch 'podhrmic/master' into chibios
[chibios] switch back to correct version
[chibios] switch back to a repo that have to 2.6 stable
fix name of git submodule
[messages] add some descriptions again
[python] fix settings path
[ahrs] update/clean test_ahrs