Fixed the way that listings are associated to books. However It's slow and we should work on improving the speed by changing the temporary booklist to a hashmap using the book_id as a key
Implemented a rudimentary infinite scroll in the BooksFragment
Added a loading spinner for when loading data. Kinda hacky, but ah well
Infinite scroll now actually adds a row in the ListView
Added infinite scroll for ListingsFragment
Merge branch 'infinite_scroll' into expand_listview