This can serve as a useful example for how to add themed icons as resources.
This will let us explore the (non-)interaction between help overlays and editing shortcuts.
We move our menus.ui file into Gtk's namespace so that it will get picked up. Accordingly, we no longer have to do any of the work for ourselves... https://bugzilla.gnome.org/show_bug.cgi?id=722092
https://bugzilla.gnome.org/show_bug.cgi?id=722092
