Bug 21479: Fix remove from cart links at the OPAC (should remove only 1)

Bug 21479: Fix remove from cart links at the OPAC (should remove only 1)

This patch changes the way biblionumbers are passed to the cart script
for adding and removing single items. The title's biblionumber is now
stored in a data-attribute on the links for adding and removing. This
should be a more robust, unified way to handle these single-item
operations.

To test, apply the patch and enable the opacbookbag system preference.

Test adding and removing items from the cart from various pages using
various methods:

 - By clicking an "Add to your cart" / "Remove" link in search results
 - By clicking an "Add to your cart" / "Remove" link on a detail page
 - By checking boxes in search results and adding via the dropdown

Each operation should work correctly.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>