Enhancements and bug fixes.

[xianglin1998]

1. In references grouping mode, we can select a single reference to highlight.
2. Fixed the bug where the canvas highlight does not disappear when switching to Dark mode or deleting filters.
3. Each reference now is an independent button and does not affect the highlighting of the filter.
4. Switch the selected row to clear all highlights before, and you can select all refs/multiple refs/single ref at once.

[xianglin1998]

[crazy4volvo]

In my tests these commits break Netlist mode. Clicking a pad/track causes dragging the board instead of highlightning a pad/track and corresponding net in the table.
Surprisingly highlightning a pad/track is possible in Grouped BOM and Ungrouped BOM modes, but of course without highlightning a net in the table which is not displayed.