Enabled POP3S for old-timeys who dig that

added dovecot-pop3d
allowed in the firewall
monitored with monit
added relevant tests
Enabled unattended-upgrades

This works on Debian/Ubuntu only.

There are similar packages for other distributions, but they still
need manual configuration. It seemed better to go for the common
denominator. unattended-upgrades is usually installed by default
anyway, so we are just reinforcing best practices.
Merge pull request #134 from tilsammans/unattended-upgrades

Enabled unattended-upgrades
Merge pull request #133 from tilsammans/pop3s

Enabled POP3S for old-timeys who dig that