Move the touchscreen switch to the other debug switches, and
move the hidpi spin to the other graphical controls. Since the
Visual tab is getting large, make it scroll. The General tab
is purely informational again.
Moving the inspector into libgtk lets use reuse internals without
having to add public API for everything or inventing awkward private
call conventions.
https://bugzilla.gnome.org/show_bug.cgi?id=730095
