Plus many load/save fixes

Scrolling was going up under title bar

I've also changed it so it reacts to hover events (changing the opacity in the process).

Removed incorrect Vehicle.altitudeWGS84

Plumb through initial object mode on Vehicle

They were causing variable scoping conflicts. This in turn caused the
widget to not update. Active property is not needed since the handling
of active/inactive vehicle is handled outside of the control

- Moved all MavManager functionality to Vehicle
- Updated all code to use Vehicle instead of MavManager
- Removed MavManager