Improve object list performance when sorting

When the object list is sorted, appending to the ListStore model is very
slow, as noted in the referenes below. To increase the performance, lets
disable the ordering while adding the objects, making it a lot more faster.

References:
   http://www.pygtk.org/pygtk2tutorial/sec-TreeModelInterface.html#sec-LargeDataStores
   http://faq.pygtk.org/index.py?req=show&file=faq13.043.htp
   http://stackoverflow.com/questions/3547743/gtktreeview-insert-update-performance-penalty-because-of-sorting

Change-Id: I98f2e0a181378c0bdeacfcbdf8be6f7b115ee5c5