title: Gtkmm - Hiding a window without closing the application
body: <p>How do i hide a toplevel window without closing it?</p>
  
  <p>NdmWindow is a class inherited from Gtk::Window.
  I have added the instance of NdmWindow to Gtk::Application.</p>
  
  <p>Now, how do i hide it instead of closing it?</p>
  
  <p>Thanks in advance..</p>