started work on cart. fixed bug with login

Fixed bug with out of memory with BookActivity image. Added some matetial icons

Fixed bug with filter

now price range stores values

Now language filtres stores checked boxes

Now Genres filter keeps checked items

Now filter WORKS!!! Also JSON parameter is converted to string and saved in SharedPreferences

Added CustomJsonArrayRequest and changed Volley request in BooksFragments

fixed bug with disappearing check in languages

Fixed bug with dissapearing checkbox's state

added filter by price layout

filter_genres now retrieves genres

Started work on filter activity

added progressbar

fixed requests for all books and for one book