media-plugins/gst-plugins-gtk: GStreamer video sink rendering on a GtkWidget

media-plugins/gst-plugins-gtk: GStreamer video sink rendering on a GtkWidget

This was previously part of gst-plugins-bad via USE=gtk, but has been promoted
to gst-plugins-good upstream and the new version is packaged properly as a
split package, which also nicely keeps away the opengl flags sync mess from
gst-plugins-good main package (very few packages use gtksink to date).
Due to the code being part of gst-plugins-bad before, its KEYWORDS is copied
for faster migration of consumers away from gst-plugins-bad[gtk] to the new
package.

Package-Manager: Portage-2.3.40, Repoman-2.3.9