Stop returning a 500 Internal Server Error when the hourly updater has not run for 6+ hours

When the hourly updater has not run for 6 hours or more, the server responds to all queries with a 500 Internal Server Error. This seemed to be a good idea, because users would tell us when the hourly updater was broken and we could fix it. But actually, it's a really bad idea, because there are valid cases when we need to stop the hourly updater, for example, for making backups. Last night's backup took 10 hours, which is not really sane, but which is not a good reason to break the service for all clients. I also have a Nagios check in place that warns me when the hourly updater stops running, so that I don't rely on poor users to find out when things are broken and tell me.

The suggested change is to just serve whatever data is available, regardless of when it was written. Usually, it would be less than two hours old. But we might also serve 5 hours or 25 hours or 100 hours old data. It would be up to clients like Atlas and Globe to warn their users that the displayed data is outdated.

I'm not implementing this right now, because I want to give the Atlas and Globe maintainers the chance to add such warnings to their applications. I'd want to implement this in a month from now, if possible.