Bug 16490 - Add an "add to cart" link for each search results in the staff client

Bug 16490 - Add an "add to cart" link for each search results in the staff client

This patch adds an "add to cart" link to each line of search results in
the staff client.

To test, apply the patch and clear your browser cache if necessary.

- Enable the intranetbookbag system preference.
- Perform a search which will return multiple search results.
- Each result should have an "Add to cart" link.
  - Clicking the "Add to cart" link should add the title to the cart,
    triggering the correct pop-up message and changing the link to read
    "In your cart (remove)."
  - Clicking the "remove" link should remove the title from your cart
    and trigger the correct messages.
- Add multiple titles to your cart and perform the same search again.
  Each result should correctly indicate which titles are already in your
  cart.
- Open the cart popup window.
  - Check the checkbox for one or more titles in your cart and choose
    "Remove." The titles should be removed, and the "In your cart" label
    in the search results page should reflect that the titles are no
    longer in the cart.
  - Choose "Empty and close." All titles in the parent page should now
    indicate that they are not in the cart.
- Disable the intranetbookbag preference and confirm that the "Add to
  cart" links are no longer there.

Followed test plan. Works as expected.
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>