Move back to XCode 9.2

Move Linux to Qt 5.11.3

Add support to receive NMEA streams via UDP

Fix startup crash on initial font change signalling qgc reboot required

Camera and Video Streams

Fix startup crash on initial font change signalling qgc reboot required

Keep track of recording time if camera doesn't provide it.
Make sure camera info is received (if camera ACKs the request)
Keep track of camera's heartbeat. Remove camera if not heard from after a while.
Update MAVLink

Allow plugins to control mainQmlWidgetHolder creation.

Check if qgcApp() actually exists before using it.

Video fit and camera pinch zoom

Remove the concept of reserved buttons for manual control

Plan: AltMode visual tweaks

AltMode visual tweaks

Default abort alt = 0. This works around problems between multi-rotor and fixed wing

Toolstrip tweaks

Default abort alt = 0. This works around problems between multi-rotor and fixed wing.

Joystick Video/Camera control