CardListView setAdapter can cause ambiguous method calls.

While working with a Loader and implementing the `onLoaderReset` method I attempt to call `CardList.setAdapter(null)` which causes a compiler error: 

Error:(171, 16) error: reference to setAdapter is ambiguous, both method      setAdapter(CardArrayAdapter) in CardListView and method setAdapter(CardCursorAdapter) in CardListView match

I've attempted to cast null to one of these ```setAdapter((CardArrayAdapter)null)```, but that did not work as desired.  

In reviewing the source code there are three overloaded versions of setAdapter:
1. setAdapter(CardArrayAdapter)
2. setAdapter(CardCursorAdapter), 
3. setAdapter(ListAdapter).  

Both the CardArrayAdapter and CardCursorAdapter are decedents of the generic ListAdapter, and the implementation of the setAdapter method is identical for both types.  This pull request changes the CardCursorAdapter and and CardArrayAdapter overloads to be private and use different method names (setCursorAdapter and setArrayAdapter respectively) so that the generic ListAdapter method takes precedent.