gst/mxf/: Implement parsing of Event Tracks, Static Tracks, DM Segments and DM Source...

gst/mxf/: Implement parsing of Event Tracks, Static Tracks, DM Segments and DM Source Clips as a preparation for desc...

Original commit message from CVS:
* gst/mxf/mxfdemux.c: (gst_mxf_demux_handle_metadata_track),
(gst_mxf_demux_handle_header_metadata_resolve_references),
(gst_mxf_demux_handle_metadata):
* gst/mxf/mxfparse.c: (mxf_metadata_track_parse),
(mxf_metadata_structural_component_parse),
(mxf_metadata_structural_component_reset):
* gst/mxf/mxfparse.h:
* gst/mxf/mxftypes.h:
Implement parsing of Event Tracks, Static Tracks, DM Segments
and DM Source Clips as a preparation for descriptive metadata
support. Next step is to implement SMPTE S380M, "Descriptive
Metadata Scheme-1".