Bug 26686: Fix sorting of "updated on" and "time created" on notices tab

Bug 26686: Fix sorting of "updated on" and "time created" on notices tab

In the patron's account in the staff interface there is a tab
'Notices' that shows all notices sent out to a patron. The
updated on column would not sort at all, but there was also some
markup missing for the time created column.

To test:
- Make sure you have a patron account with some notices, ideally
  with different times and dates
- Verify that the updated on column doesn't sort at all
- Apply patch
- Verify both date columns now sort correctly for different
  DateFormat settings

Signed-off-by: Séverine QUEUNE <severine.queune@bulac.fr>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>