Moving source files into Vehicles as it is a more coherent place.

Forcing QGC to use Mavlink V2 if vehicle supports it.

* Mavlink/master:
  Only run unit tests on pull requests
  MAVLink: Update to most recent spec
  PX4 param and airframe metadata update (#4169)
  Don't apply throttle deadband in ThrottleModeDownZero
  Use FTDI driver provided by ftdicjip.com
  AppImage update to libsdl2 (#4155)
  Minor formatting fix
  Added a second polygon. This polygon is updated from the first polygon at each mouse click and is what will ultimately be saved upon completion of drawing.
  Fixed a bug where a black line would be rendered when starting to draw a polygon.
  Fix brand image visibility calculation
  Remove FileManager unit test
  VTOL text change
  Update VTOL command text
  Update message
  Temp removal of Onboard File
  Changing label
  Making deadbands stupid-proof; general cleanup
  Cleanup & Sync
  Implementing throttle axis accumulator with deadband support
  Handle redirects in file downloads

Implementing throttle axis accumulator with deadband support

Use FTDI driver provided by ftdichip.com

- Fixes lost connections with FTDI radios
- Modified code to only test vendor id, all product ids are let through
- Modified code to pass log output through to C++ side
QGCLoggingCategory system

Multicolored polygon

Fix brand image visibility calculation

Temp removal of Onboard Files

- fixes #4148

Added a second polygon. This polygon is updated from the first polygon at each mouse click and is what will ultimately be saved upon completion of drawing.

Update VTOL command text

Update message

Too buggy to leave in for now

Fix line back to home for VTOL takeoff

Adjust incoming message on channel 0

SDL2: Add missing Info.plist file for SDL2 framework.