Fixed sorting bug

1) removed the hack code that held onto the fragments.  It now get's the
fragment from the view adapter using instantiateView(position).
2) The TodoPanelFragment now uses onSaveInstanceState to save the name
of the list, so it can restore it when the fragment is recreated.
3) Changed TodoActivity so it saves whether the data has been loaded in
onSaveInstanceState() so it can know in onCreate() whether it should
load it again.  This is what fixed the sorting bug.