[feature request] HEK - organize the selector by what is visible

[Jack Ireland]

For any given time, the HEK F/E selector can have every event type selected, but typically only very few of the possible event types are actually in the viewer window. We could organize the HEK F/E selector by events in the viewer window/ events not in the viewer window. All F/E types that are not in the viewer window would be collected in to a tab that could be opened so the user could see what is to be displayed or not.

This would mean that the HEK F/E selector would be more dynamic as the event visibility changes from time to time. It would make the F/E selector much more compact and tidier looking. Its default view would be to show you only the events which are actually in the viewer window, without the added visual clutter of all the things that are not in the viewer window but you might see at another time.