Bug 31939: Add page-section to branches template

Bug 31939: Add page-section to branches template

This patch adds the page-section class to the appropriate blocks in the Libraries administration area.

Test plan
1) Confirm that Administration > Libraries correctly displays the table
   inside a page-section card
2) Confirm that Administration > Libraries > 'A library' correctly
   displays a card for the main information at the top and a separate
   card for OPAC Information if added.
3) Confirm that the 'Add' and 'Edit' library forms still look good.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>