Add support for geofence return point. Also fixed a bunch of bugs in geofence and rally point support.

Move all airmap related stuff to its own directory

- 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)

This is just to test, will need much better integration

This time to handle correctly updating plan/fly view when plan changes

- GeoFence support comes from plugin
- Circle fence support
- Better param support