title: Custom python widgets in glade 3
body: <p>I would like to subclass an existing Gtk widget and get it to work with Glade3.  The code is all python, and I'm using PyGObject.</p>
  
  <p>What I want to do is extend Gtk.TextView and be able to add it to my glade UI as if it were a native widget.</p>
  
  <p>I read that it was possible with Glade 2, but I'm not sure how to do this with Glade 3, and I can't seem to find any examples or documentation on this.  Any help would be appreciated.  Thanks.</p>