Bug 14194: Restore the HH:MM to 23:59 for onsite-checkouts

Bug 14194: Restore the HH:MM to 23:59 for onsite-checkouts

(Introduced by bug 13601)

Test plan
=========
1/ enable 'OnSiteCheckouts' pref under Circulation Preferences
2/ go to the checkouts page and try to issue an item to any user.
3/ when the item barcode entry form shows, select the 'On-site
   checkout' checkbox
4/ the default date due should show as today with 00:00 as HH:MM
5/ apply the patch
6/ repeat steps 2 - 3. The default date due should show today's
   date with 23:59 as HH:MM.
7/ run koha-qa.pl -c 1 -v 2

Remarks: Testing result match expected test plan output. The QA tests
         pass with "OK" for the commit.

Technical note: There is a confusion with iso and sql date formats at
some places in the code.
A better way should be provided (later) to fix globally the mismatch
between these 2 formats.
What happened before this patch: the DateTime was cast to a string and
the template received "YYYY-MM-DDTHH:MM:SS" which is an iso formatted
date. BUT this format is not managed by Koha::DateUtils::output_pref
("iso" and "sql" are considered as indentical which is wrong).
As I did not estimated the problem (how big it is) I prefer to fix it
easily (and dirty) for now.

Signed-off-by: Indranil Das Gupta (L2C2 Technologies) <indradg@gmail.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>