Rationalise trailing slashes from admin_base_url

Remove from admin_base_url (which wraps config vars like
{ADMIN_,}BASE_URL) and add to places in code which aren't
expecting it.
Test for admin_base_url in RS::Problem

Test that the slash is added in correct place (the base URL should not
have its own trailing slash).
[Zurich] stats export include 'hidden'

See https://github.com/mysociety/FixMyStreet-Commercial/issues/461

Again, we just need to substitute the %params line (which elides
hidden reports) for the less restrictive %date_params.

This commit includes very basic tests for the previously untested
?export=1 functionality.
Merge branch 'issues/commercial/460-trailing-slashes-on-base-url'
Merge branch 'issues/commercial/461-zurich-export-hidden-stats'
.gitignore for conf/crontab

This is required after changes in
59eb44959e9cb8ccd21e9be813e4d1c8baaa1dcc for mySociety internal
deployment toolchain.
[Zurich] admin template to respect closed_overdue

This value is now cached, but the template calls the function,
calculating it anew, so for old reports (closed within SLA) the
problem_row.html template showed these as overdue.  Instead, we point
the template at a function which first checks the cached value.

(Attempting to roll this functionality into the .overdue() method itself
caused a fair amount of collateral test breakage, and it seems safest to
extract the caching function for now.)

Closes https://github.com/mysociety/FixMyStreet-Commercial/issues/462
Merge branch 'issues/commercial/462-zurich-overdue-row-colour'
Merge remote-tracking branch 'upstream/master'
Merge branch 'master' into baiki