This lets roundcube's manageseive plugin do cool things like vacation responses.
Also:
* Run the spam filtering sieve script out of a global sieve file that we'll place in /etc/dovecot. It is no longer necessary to create per-user sieve files for this. Remove them with a new migration. Remove the code that created them.
* Corrects the spam script. Backslashes were double-escaped probably because this script started embedded within the bash script. Not sure how this was working until now.
this adapts work by @h8h in #103
* for local mail users, also disallows periods at the beginning or end of the local or domain parts
* Dovecot gets confused if the string contains any unusual characters, so local mail users are restricted to a narrow regex
* for mail aliases Postfix is not confused so use a regex based on RFC 2822
* Created a new Python/flask-based management daemon.
* Moved the mail user management core code from tools/mail.py to the new daemon.
* tools/mail.py is a wrapper around the daemon and can be run as a non-root user.
* Adding a new initscript for the management daemon.
* Moving dns_update.sh to the management daemon, called via curl'ing the daemon's API.
This also now runs the DNS update after mail users and aliases are added/removed,
which sets up new domains' DNS as needed.
