For Video Streaming usecase, QGroundControl doesnt support changing of
Video Source or URI settings. Restart of QGroundControl application was
required for the changes to get applied. The issue is now resolved by
restarting the video receiver pipeline with new video source/setting.

Signed-off-by: lbegani <lalit.kumar.begani@intel.com>

And fix broken file path to save video on windows

Made QGCCorePlugin derive from QGCToolBox and expose everything through the same mechanism as everything else.