Add an email warning if 'old' submissions in queue

[thepurpleblob]

Firstly, I haven't thought this out terribly well but... it would be very useful if the plugin sent an alert (preferably to a nominated user or email address) if it looked like Urkund had ceased to receive submissions for some period of time. We're really looking to get an alert if there's a reasonably possibility that submissions are not getting processed.

[danmarsden]

Thanks Howard,

one of the issues with the design using the old events was that if a failure occurred it would stop all further events from processing - the new design doesn't have the same issue so hopefully should be a lot more reliable. The debugging page also includes some improvements around re-submissions but it still might be helpful in future for some form of admin e-mail notification - I'll keep it in mind thanks!

[thepurpleblob]

It's more to alert us if the Urkund server (e.g.) goes down - which has happened.