Handle gstreamer signals on main QGC thread to avoid deadlock; Remove video sink from pipeline if pipeline failed to start

Fix matroskamux stream start (workaround for https://gitlab.freedesktop.org/gstreamer/gst-plugins-good/issues/449)

Use parsebin for automatic stream demuxing and parsing; Automatically insert rtpjitterbuffer for RTP streams to avoid video stuttering

Switch to decodebin and use decoder with highest rank; Use GL context provided by qmlglsink; Fix JNI code for AndroidMedia initialization

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

This solves the issue where the video is lost for a few seconds  after
clicking record as the filesink attempts to preroll but doesn't have a valid buffer,
stalling the whole pipeline.

Updated MAVLink to handle video stream types (auto discovery)

On desktop (Ethernet connection), the ground unit pushes UDP directly, which makes the use of an actual "Link" not possible. Instead, I've moved all of Taisync support to a "manager" owned by QGCToolbox.
Added a Taisync settings with some basics already wired and running.