Bug 28933: Add subscription class to each subscription in opac-detail

Bug 28933: Add subscription class to each subscription in opac-detail

To Test:
1. Go to a record with some subscriptions, have some closed and some
   open.
2. Go to the opac-detail page, click on the subscription tab and use
   your developer tools to inscept the element.
3. Notice the hierarchy of HTML structure, everything is a sibling of
   the next.
4. Apply patch
5. Reload the same opac-detail page and again inscept the element.
6. Now every individual subscription should be wrapped in an element
   with the class name of 'subscription'.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>