Use named arguments instead of positional arguments with the GObject constructor
As the client will now run only on GTK3 this Deprecation Warning should be removed.
Example:
PyGTKDeprecationWarning: Using positional arguments with the GObject constructor has been deprecated. Please specify keyword(s) for "label" or use a class specific constructor. See: https://wiki.gnome.org/PyGObject/InitializerDeprecations