Android Fragments introduced 
Instead of using activities to display the list and details now we user
fragments.
MainActivity is changed to load the DiscountListFramework which then
takes over the control of the list, as the MainActivity did.
MainActivity sends an event when new data arrived. DiscountListFragment
listens to this through OnDataChangedListener and changes the data
accordingly. It is completely independent of the data source. 
DiscountExpandableAdapter is changed so that it no longer uses the
DiscountDetailsActivity, but rather a DiscountDietailsFragment. The most
of the code was reused. With this change DiscountDetailsActivity is no
longer necessary and it is removed. It's layout, became (is renamed to)
fragment_details_layout and now it is used by the fragment. (activity is
also removed from the AndroidManifest file).
Other news:
 - /anim/*.xml which contains the animations 
 - main_fragment_layout is changed to have only the container in which
you place fragments
 - fragment_list_layout is now what activity_main used to be. It is
reused and renamed. 
 - added detailed comment to the new code