Zurich: test moderated_overdue

- is set to 0 on state change within time-limit
- is set to 1 on state change after time-limit
- only marks overdue on first time
Zurich: quash undef warning on date-check
Zurich: log details for closed_overdue

see mysociety/FixMyStreet-Commercial#459 the new requirement is for
"Innerhalb von fübeitstagen abgeschlossen" - a report is dealt with
(abgeschlossen) as soon as the public state is Beantwortet (db: fixed -
council or closed) or Unsichtbar (en: Invisible, db: hidden).

Have added this as {closed_overdue} but have retained the logic for
{subdiv_overdue} logged in the %extra hash for now, in case it is
needed.
Zurich: test /admin/stats

First test that this page is only available to superuser.

Then test that the moderated and fixed stats are doing something that
is (hopefully) the spec in mysociety/FixMyStreet-Commercial#459