- Restructured a number of MissionItem properties as well

Plus lots of other cleanup

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

Signed-off-by: kai <kai@uav-flightresearch.com>

- MultiVehicleManager is a Qml friendly replacement for UASManager
- Vehicle is a replacement for both UAS and AutoPilotPlugin

- FirmwarePlugin is the new place for code which is specific to
firmware flight stack
- FirmwarePlugin currently supports flight mode apis
- Modify code to use new FirmwarePlugin support

Also restructured some toolbar positioning QML to handle resizing.