Baro event handling using ABI interface

Main benefits:
* less crappy handler functions in main.c files
* possibility to use multiple sources of sensors (integrated to the board or not)
* the filters don't need to know who is sending the raw values (not completely true with the old alt_float filter yet)

* the pressure are now standardized in Pascal and the standard atmosphere model is used
  * The INS_BARO_SENS is hence not needed anymore.
* onboard baros are automatically available in fixedwing firmware as well (use same code as rotorcraft now)
  * disable onboard baro with ```<configure name="USE_BARO_BOARD" value="FALSE"/>```

Some stuff to do before using: find the default conversion factor to convert ADC values to Pascal (mostly older boards/baro, recent digital sensors can output pressure in Pascal already)

Baro sensors/drivers that are checked to output pressure in Pascal:
- [x] bmp085
- [x] ms5611
- [x] mpl3115
- [ ] Umarim analog (MPXA6115 pressure sensor + ADS1114 16bit ADC)
- [x] Booz analog
- [ ] Lisa/L analog
- [ ] pbn (pressure board navarro, not currently used)
- [x] amsys
- [ ] ets
- [ ] ms5534
- [ ] hca
- [ ] scp