Filter by Toolkit (i.e. Qt, Gtk, etc.)

I added new filter options so you can only view apps with specific toolkits. These new options are sub-entries to the overall Show Graphical Apps option. It must be checked for the others to matter. The available toolkit options are Gtk, Qt, Tk, wxW, and other. Ncurses already had a separate callout.

Hopefully this will help those KDE and Gnome users who prefer Qt and Gtk apps over alternatives.

Thanks to Oliver for the suggestion.