title: Making a Gtk.Window not deletable
body: <p>I need a Gtk.Window that is not deletable. So if the user clicks the "close" button (every generic window has  "close", "minimize" and "maximize" buttons) the Gtk.Window shouldn't close. </p>
  
  <p>I tried <code>Gtk.Window.set_deletable(False)</code>, but it doesn't work. Do you know any workaround?</p>