Mark Stretch as EOL, add usage report

This marks Sympl 9 (for Debian Stretch) as End of Life, and adds a message to the MOTD.

This will also be sent on a monthly basis to the root user (assuming they have the mailbox redirected or read it directly) as a reminder.

This also adds a basic usage reporting system, which can be disabled by touching /etc/sympl/disable-usage-reporting. This reports basis stats such as the number of domains, mailboxes, websites, databases and count of domains using FTP/cron functionality