[GTK3] Change module structure from ui/gtkui to ui/gtk3

This moves the directory structure so that there is no conflict with the
old gtk2 UI. Also changes the conf and state files being loaded.

setup.cfg

@@ -22,7 +22,7 @@ known_third_party =
 # Ignore Windows specific modules.
     bbfreeze, win32verstamp,
 # Ignore gtk modules, primarily for tox testing.
-    pygtk, gtk, gobject, gtk.gdk, pango, cairo, pangocairo,
+    pygtk, gtk, gobject, gtk.gdk, pango, cairo, pangocairo, gi
 # Ignore other module dependencies for pre-commit isort.
     twisted, OpenSSL, pytest, recommonmark, chardet, pkg_resources, zope, mock,
     sphinx
@@ -39,7 +39,7 @@ use_parentheses=True
 [flake8]
 max-line-length = 120
 builtins = _,_n,__request__
-exclude = .git,.tox,dist,build
+exclude = .git,.tox,.eggs,dist,build
 ignore =
 # A003 Class attribute is a python builtin.
     A003,