Bug 35006: OPAC holdings table - Fix sort for library columns

Bug 35006: OPAC holdings table - Fix sort for library columns

This patch updates the holdings table on the OPAC's bibliographic detail
page so that home and current library columns can be sorted correctly by
library name. There have been changes to the way the template shows
these values, but the DataTables "data-sort" attribute on the table cell
had not been updated accordingly.

To test, apply the patch set the OpacLocationBranchToDisplay system
preference to "home and holding libraries."

- Make sure home and holding library columns are not hidden in the
  table settings under Administration -> Table settings -> OPAC ->
  holdingst.
- Locate a bibliographic record in the OPAC which has multiple items
  from different libraries.
- Test that the home and current library columns sort correctly by
  library name.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>