Delete/hide very old statistics #425
Description
#411 implements monthly statistics for messages that are archived.
Eventually, we may want to start deleting very old statistics (e.g. older than 5 years or so?). Also, the chart for monthly emails sent on the statistics currently does not have a limit on the number of months it displays. We could also choose to update the statistics API end-point to only get statistics from the last 5? years from the database.