Addresses #3
Added support by adding parallel code wherever `$PUBLIC_IP` was used.
Providing an IPv6 address is completely optional.
Playing around on my IPv6-enabled mail server revealed that — before
this change — mailinabox might try to use an IPv6 address as the value
for `$PUBLIC_IP`, which wouldn't work out well.
* 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
* adding a Vagrantfile
* in a non-interactive setup like this, create the user's first email account for them
* let the machine auto-detect its IP address using http://icanhazip.com/
* use our own justtesting.email domain to provision a subdomain for users so they can quickly get started
* 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.
