[195/906] fix gstgldifferencematte and add an example app to test it dragging an image over the video (works with pixbufoverlay too, see pixbufdrop --help)
[195/906] fix gstgldifferencematte and add an example app to test it dragging an image over the video (works with pixbufoverlay too, see pixbufdrop --help)

pexip/gst-plugins-good,GStreamer/gst-plugins-good,StreamUtils/gst-plugins-good,pexip/gst-plugins-good,GrokImageCompression/gst-plugins-good,GrokImageCompression/gst-plugins-good,GStreamer/gst-plugins-good,StreamUtils/gst-plugins-good,GrokImageCompression/gst-plugins-good,GStreamer/gst-plugins-good,StreamUtils/gst-plugins-good,StreamUtils/gst-plugins-good,pexip/gst-plugins-good,pexip/gst-plugins-good,GStreamer/gst-plugins-good,pexip/gst-plugins-good,GrokImageCompression/gst-plugins-good