Bug 23955: Replace famfamfam icon in OPAC holds template

Bug 23955: Replace famfamfam icon in OPAC holds template

This patch modifies the OPAC holds template so that when an item isn't
available for an item-level hold a Font Awesome icon is displayed
instead of a famfamfam image.

To test, apply the patch and regenerate the OPAC CSS
(https://wiki.koha-community.org/wiki/Working_with_SCSS_in_the_OPAC_and_staff_client).

 - Make sure you have items which can be placed on hold at the item
   level.
 - Locate a title with more than one item, at least one of which isn't
   available to be placed on hold (item is marked withdrawn, for
   instance).
 - Start the process of placing a hold on the item.
 - On the "Confirm holds" scren, click "Show more options" and select "A
   specific item."
 - In the table of items, any item which isn't available to be put on
   hold should be inidicated with a red X. The title attribute of the
   icon should show "Cannot be put on hold."

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>