gst/matroska/: Extract palette data for dvd subpicture streams and send it downstream...

gst/matroska/: Extract palette data for dvd subpicture streams and send it downstream as custom gstreamer dvd event (...

Original commit message from CVS:
Patch by: Mark Nauwelaerts <manauw skynet be>
* gst/matroska/matroska-demux.c:
(gst_matroska_demux_push_dvd_clut_change_event),
(gst_matroska_demux_parse_blockgroup_or_simpleblock),
(gst_matroska_demux_subtitle_caps):
* gst/matroska/matroska-ids.h:
Extract palette data for dvd subpicture streams and send it
downstream as custom gstreamer dvd event (fixes #453417).