Bug 19338: Fix sorting by dates in opac-account.tt

Bug 19338: Fix sorting by dates in opac-account.tt

To test:
Find an account with lots of fines/payments
load up the borrower's account in the OPAC
note that the sort on the dates sorts by day, and not by date.
apply this patch
reload the page, note that the sort on the dates is now correct.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Alex Arnaud <alex.arnaud@biblibre.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>