Use accessor functions for data fields

The following data fields that were provided by PyGTK are not accessible
directly in GTK3+pygi and need to be replaced by accessor calls:

Adjustment.lower
Adjustment.page_size
Adjustment.upper
Adjustment.value
Bin.child
Widget.parent
Widget.style
Widget.window

Based on patches by Daniel Drake <dsd@laptop.org>.

Signed-off-by: Sascha Silbe <silbe@activitycentral.com>

src/sugar3/activity/activity.py

@@ -901,8 +901,8 @@ class Activity(Window, Gtk.Container):
             self.reveal()
 
     def __realize_cb(self, window):
-        wm.set_bundle_id(window.window, self.get_bundle_id())
-        wm.set_activity_id(window.window, str(self._activity_id))
+        wm.set_bundle_id(window.get_window(), self.get_bundle_id())
+        wm.set_activity_id(window.get_window(), str(self._activity_id))
 
     def __delete_event_cb(self, widget, event):
         self.close()