[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
[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)
[tmtc] ivy2nmea doesn't need gps lib, remove it on clean
[sys_time] maximum of 16 sys_time timers by default (was 8)

actually makes the baro periodic timer (for BARO_BOARD) usable by default on fixedwings
[settings] remove settings from automatically unloaded modules
[modules] fix modules' settings
[ocaml] md5 sum target dependent due to unloaded settings
[baro_board] ms5611, error if BARO_PERIODIC_FREQ is over 100