Bug 26761: Use aria-disabled attribute in OPAC cart for disabled links

Bug 26761: Use aria-disabled attribute in OPAC cart for disabled links

This patch adds "aria-disabled" attributes to disabled links in the
Cart, and adds JS to change the value from "true" to "false" when the
links are enabled. The goal is to make the interface more informative to
users of screen readers.

To test, apply the patch and add some items to the Cart in the OPAC.

- Inspect the markup of controls like "Remove", "Place hold," etc. Each
  should look disabled (grey) and has the correct aria-disabled
  attribute value.
- Select one or more checkboxes. The links should be come active, and
  the aria-disabled attribute shoulk now be "false."
- Deselect all checkboxes. The links should now be disabled.

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>