Made the highlight box extend over the exon view (previously it was just shown...

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.