Add Supybot (IRC bot) service

This adds a basic service for supybot, an IRC bot. Configuration is typically done by means of a script: supybot-wizard, so I haven't attempted to add individual configuration options.

This is my first attempt at writing a service module, so feedback would be great! I failed to set the stateDir to /var/lib/supybot by default since it caused useradd to fail. I have tested it using build-vm.