Support real highlighting (without the creation of a note)

Please add a feature to highlight text without creating notes every time. Maybe by adding an option to the custom highlight definitions "create note/don't create note" (technically it could be an invisible note-entry or something like that - keep it simple and doing it this way makes "converting" a highlight to a note simple). And please add customizable icons/iconcolors for the custom highlightings icons used in context menus and smaller areas (right now every custom highlight gets an gray icon - all get the same one).