Fix broken maintenance mode
Maintenance mode has been broken since r7fe19ebfe0d3 (Thu Jun 4)
"Display caught errors on the page itself", fix it by passing the
site entity, rather than the site module to isActivePeriod.
Fix 500 when saving /site/edit without email
When saving /site/edit with no no_reply_email set, a 500 error page
would be returned due to an empty value being passed as value to
the datastore (which is not allowed for email fields).