When opening pavucontrol.glade with Glade 3.22.1, this message was
shown:
pavucontrol.glade targets Gtk+ 2.16
But this version of Glade is for GTK+ 3 only.
Make sure you can run this project with Glade 3.8 with no deprecated
widgets first.
I think it's best to just drop the gtk2 support.