[settings] improve settings in pprzcenter

- check box for faster enable/disable
- loading from modules
[settings] add a few more settings in modules
[settings] variable size modules settings area
[settings] add settings directly inside modules files
[settings] allow several groups of settings in modules
[settings] move settings to module files and remove old files
[settings] fix example conf
fix conf_example
remove another unneeded settings file
[FBW] Compile less overhead in FBW
[FBW] no need for i2c when there is no i2c
[modules] add missing default case in cam
[generators] gen_airframe: don't force float if unit = code_unit
[conf] update CDW airframe with chimu/cam
possibility to pass ref to paparazzi_version
[fixedwing] Option to have telemetry through the FBW

- for outback safety (so it can decode flight termination modes even when AP is down)
- Keep datalink while in flight termination mode

closes #844
[settings] select new modules' settings by default
[ocaml] remove leading white space when get tree values
[conf] update all example airframe for new modules' settings
[baro_board] make configure work for BARO_PERIODIC_FREQUENCY (needed to use define before)