Bug 31209: Add a span with a class for items.enumchron in the checkouts list

Bug 31209: Add a span with a class for items.enumchron in the checkouts list

To test:
* Add or edit an item and add some info to the 'Serial Enumeration /
  chronology' field
* Check the item out
* Verify by checking the source code or using the element inspector
  that the title and enumchron have been merged into one string
* Apply patch
* Reload and verify that now the enumchron is wrapped in a span
  with class="item_enumeration" matching the class in the list of
  checkins

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>