ext/ffmpeg/gstffmpegcodecmap.c: Generalized palette functions, add actual mimetypes for wing commander formats.

Original commit message from CVS:
* ext/ffmpeg/gstffmpegcodecmap.c: (gst_ffmpeg_codecid_to_caps),
(gst_ffmpeg_caps_with_codecid), (gst_ffmpeg_caps_to_codecid):
Generalized palette functions, add actual mimetypes for wing
commander formats.
* ext/ffmpeg/gstffmpegcolorspace.c: (gst_ffmpegcsp_chain):
Ffmpeg has internal palette functions, so I noticed.
* ext/ffmpeg/gstffmpegdec.c: (gst_ffmpegdec_chain):
Actually remove all palette code.