Retry in all the right/possible places. Don’t freak out about things
coming in unknown sequences.

Change in visibility was causing combo box contents to reset. Visible
goes to false even when you move away from Plan view, not just when the
combo is unused.

- Incorrect signaling causing dirty but to be incorrect
- Remove all not working
- Min fence point count incorrect

This gets it above your head

Moving source files into Vehicles as it is a more coherent place.

Forcing QGC to use Mavlink V2 if vehicle supports it.

This makes it available on mobile builds

Added a second polygon. This polygon is updated from the first polygon at each mouse click and is what will ultimately be saved upon completion of drawing.