Re-fire automatic checks

[Per Hallgren]

If a check failed because of an issue with hardware, a bug, or another submission that crashed/exhausted resources, the check should be re-issued when the situation is resolved. This could be either automatic (re-run pending checks every hour), or it could be solved with a manual re-check button (which is disabled for X minutes after submission?).

[Evgeny Kotelnikov]

How about this:

1. For every submission Fire makes up to three attempts to request a check, let's say the requests are five minutes apart.

2. If all the attempts failed, the check is marked as "invalid" and is displayed with the message "Was not able to run automatic check".

3. Invalid checks are shown in the admin interface (together with the log info from #133).

4. There is a button in the admin interface that reruns all invalid checks.

That way, if you encountered a bug that messes up the checks, or the check server is down all together, you notice that by seeing invalid checks. Once the problem with the server is resolved, you re-run all the checks that need to be rerun with the click of one button.

[Per Hallgren]

I think this sounds good!