Made QGCCorePlugin derive from QGCToolBox and expose everything through the same mechanism as everything else.

Signed-off-by: Tomaz Canabrava <tomaz.canabrava@intel.com>

Removed incorrect Vehicle.altitudeWGS84

Plumb through initial object mode on Vehicle

- Positions are bounded to rectangle
- No longer re-centers if thumbs go outside bounds
- ThumbPad moves to meet first thumb position, this prevents
inadvertent movement as you put your thumb down

Also remove concept of “interactive” since it is no longer needed

Also show QGC position on map

Windows OS doesn’t disconnect port when you pull plug on USB. This
caused all sorts of problems with previous logic. New logic handles
this correctly.