Add autoreply filter concept

**mail-autoreply** is a simple filter which allows an administrator to configure a list of regular expressions executed against the subject and body of incoming emails (piped and fetched). If any match, the mail is flagged as an automated response and will instruct osTicket not to send returning automated responses.

This is a fair last mile for automated responses which either have no connection to previous messages or do not use a MIME header to indicate they are automated.

**This plugin requires extra code in osTicket** See osTicket/osTicket-1.8#958