[gcs] specify max map zoom level with -maps_zoom option
- defaults to 18, max is 22
  - TODO: check that a valid zoomlevel was given
  - add it to the menu to change at runtime?
- if available, larger (low zoomlevel) tiles in cache are loaded right away,
  even if higher zoomlevel maps could be downloaded.
Care Free mode
care_free_heading in stabilization.c
Baro MS5611: add nav.h for ground_alt (although not used), change
I2C address to 0xEE for CSB\ low (as in most boards as Aspirin2.1,
FreeIMU 0.4.3, ...)
[rotorcraft] add CareFree mode to settings/gcs
[rotorcraft] care free mode

- still not implemented for stabilization_euler
- move read_rc_setpoint_* functions to c file
- add GUIDANCE_H_MODE_CARE_FREE mode
- add stabilization float_euler subsystem
- use normal stabilization subsystem in NPS instead of hardcoded euler
[imu] aspirin2: suppress unused arg warning
[stm32] convert SpektrumParser from macro to static inline function
Add centidegrees
Add Aeroprobe On-The-Fly! air data computer interface
naming foo
[modules] minor prettify
care free mode for euler
removed todo euler care free
improved care free euler
[settings/gcs] save and display settings as integer if step is integer

close #381
[sonar] some fix for sonar module

sonar_scale is now a float in m/adc
fixed misplaced brace
[gcs] display settings to be saved as integer with correct format
[gcs][settings] nicer popup warning about parameters not in the airframe file