Show last update date+time for counters
The counters on the main page are no longer updated in real time (see #726). It would be nice to be able to see the time when the counters was last updated. If possible, a link for forcing a new count could be active if the counters are older than a limit (for example, 5 minutes). Note that the counters are automatically updated every hour so the limit should not be longer than that.