Merge branch 'master' into ahrs_refactor

* master: (86 commits)
  [ahrs] update/clean test_ahrs
  [python] fix settings path
  [messages] add some descriptions again
  fix name of git submodule
  [chibios] switch back to a repo that have to 2.6 stable
  [chibios] switch back to correct version
  [ocaml] filter for 'field' tag when looking at messages
  [submodules] updated to a new chibios repository
  [messages] remove description node again for now
  [modules] mission_rotorcraft: only check for ned_initialized_i
  [modules][messages] mission: LLA waypoints in 1e7deg instead of float
  [build] don't compile natnet if not needed
  [messages] possibility to add descriptions
  [modules] rename flight_time to time_countdown
  [sim] remove launchsitl symlink
  [rotorcraft] navigation: fix NavCircleCount
  [modules] rotorcraft_cam: fix DEFAULT_MODE
  [omap] start basic spi driver
  [rotorcraft] arming: only check if motors can be armed if ahrs_is_aligned
  [rotorcraft] force MODE_STARTUP instead of KILL until ahrs is aligned
  ...