Notify user that he has successfully requested a book.

This doesn't mean that request is accepted, just that request is
created and sent to the owner of the book.
Don't create duplicate BorrowRequests.
Add logic for handling book borrow request.

Owner of the book can accept or reject book borrow request.
Add username next to borrow request on request list.
Add "My Books" filter on the Book list.
Bugfix - assign book borrower based on borrow request.

Previously book borrower was assigned based on currently logged
in user, which is actually the owner of the book.