Made the highlight box extend over the exon view (previously it was just shown on the grids, which is not adequate now that the exon view can be bumped and can take up quite a large area). To facilitate this and make it less cluttered I changed the highlight box from a blue outline (shown separately on each grid) to a shaded region that spans across all of the visible big picture widgets.

Fixed some bugs with the GFF3 parser. Added the 'R|r' option back in (to show/hide the reverse strand grid)

Added GFF3 parser. Removed g_prefix_error and g_propagate_prefixed_error because they're not in our current linux GTK version

More refactoring of parser code. Fixed a bug where an invalid match frame was being set when reading old format exblx files

Added a proper MSP type. Separated this out from the data type used by the parser, which is only used to record what kind of data is currently being parsed.