install modoboa, dovecot and postfix

A lot of changes, but

- modoboa is accessable via mail.192.168.99.10.xip.io
- supervisor is accessable via supervisor.192.168.99.10.xip.io
- modoboa runs in debug, because I still need to make a template for the settings.py and set the allowed_hosts

I'm setting up a demo in the cloud, this should be working tomorrow, and then we can really start testing.