Added an "unknown" weather icon for when I get "valid" data and no icon

Break apart string of classes into their own files as all in one file became unwieldy
Expose Airspace data in a QML ready format
Split global Airspace from AirMap (Only now I figured out the reason for the pure virtual root classes)
Refactored a bunch of things to make it consistent and/or obvious

Move all airmap related stuff to its own directory

You need to adjust the 'AIRMAPD_PATH = path_to_airmapd' in
qgroundcontrol.pro to make it compile.

And sorry for the huge commit :/

- add multi-vehicle support: each vehicle has now a per-vehicle AirMap
  object that takes care of flight creation, traffic & telemetry
- add a base class API layer so that the interface between QGC and the
  AirMap implementation is clear, and easier to change
- removes polygon upload to vehicle (needs a better solution)

Added AirMap settings (SettingsGroup)
Added AirMap settings block to General Settings
Create macros to deal with the tedious repetitions within SettingsGroup
Removed old, hacked in setting for AirMapKey
Remove a few of the tons of build warnings

This includes polling for a flight permission.
The steps are:
- get pilot id (new API requires to provide it, even though it does not
  make much sense)
- create a flight plan
- call the briefing (to check if SITA registration id's are valid)
- call the submit -> returns the actual flight id
- poll on the briefing until the flight gets approved

Since there can only be one flight, on startup, we list the pilot's flights
and end the one that ends in future

- start telemetry if there's a valid flight id and the vehicle armed
- only the Position message is sent for now