activeVehicle - >_activeVehicle
caused the virtual joystick to malfunction

Clean up references to MainRootWindow globals

LinkInterface and Vehicle uses mutexes to synchronize writing bytes to the link instead of queued signals

Cherry pick virtual joystick fix from Stable

Rework Fly View into separate layers which can be customized at each layer.

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

Fixed flight widget position.