Show archive log date for archived caches

[FriedrichFroebel]

To better estimate whether logging an archived cache, we might consider showing the date of the archive log. This is especially recommended when the log to post is dated after the archive event.

The OKAPI does not provide us with this information (the date of the last modification does not have to be correct), so we would probably have to search the log entries of the cache until we find an archive log if the cache actually is archived at the moment.