- Added menu options to select new mode as well as new settings and defaults

Adding mux GStreamer plugin libraries to Android (to enable video recording on Android)
Adding an option to limit the amount to disk used for saving videos
Adding an option to show/hide the REC button (allowing plugins to handle the recording in their own way)
Adding simple frame grab to file

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.