[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
[abi] add TEMPERATURE message
[modules] baro modules publish TEMPERATURE via ABI
[modules] ms45xx publishes BARO_DIFF and TEMPERATURE via ABI
[math] pprz_isa: QNH functions
[air_data] use ABI for differential pressure, compute airspeed from it
[air_data] add qnh and amsl
[modules] make air_data a module
[airframes] add air_data module to some example airframes
[air_data] add TEMPERATURE ABI message and calc true airspeed

- removed airspeed_scale
- true airspeed (TAS) factor calculated from pressure and temp
  - if that is not available, tas_factor can be set manually (and could be used to replace airspeed_scale