Bug 35124: Incorrect item groups table markup

Bug 35124: Incorrect item groups table markup

This patch corrects the markup of the item groups table which is found
under the "Item groups" tab on the bibliographip detail page in the
staff interface.

The patch also adds the "NoSort" class to the "actions" column to
prevent it from being sortable.

To test, apply the patch and make sure the "EnableItemGroups" system
preference is enabled.

- In the staff interface, locate a record with items and view the detail
  page.
- Under the "Item groups" tab confirm that the table looks correct: The
  heading labels should be centered bold text.
- You should see sorting indicators on the "Display order" and "Description"
  headings but not on the last one.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>