Bug 25832: Add DataTables to MARC subfield structure admin page for authorities

Bug 25832: Add DataTables to MARC subfield structure admin page for authorities

This patch adds DataTables sorting and filtering to the table of
subfields shown on the Authority MARC subfield structure administration
page.

To test, apply the patch and go to Administration -> Authority types.

 - From the 'Actions' menu, select 'MARC structure.'
 - From the 'Actions' menu, select the 'Subfields' link for a tag
   with multiple subfields.
   - On the page showing all the subfields for the tag, confirm that
     the table is sorted by default by subfield and that sorting works
     correctly.
   - Confirm that the search form at the top of the table works.

Signed-off-by: Katrin <katrin.fischer@bsz-bw.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>