gio2: add Gio::Dbus module

This module contains Gio DBus Utilities methods such as:
* ganerate_guid
* is_*

ref: https://developer.gnome.org/gio/2.42/gio-D-Bus-Utilities.html

(Gio::DBusUtilty or Gio::DBusUtilties is more appropriate for this
module name?)