This allows you to select and configure the service without
touching the main compose file, making updating a lot easier.

Also add overrides for MyDNSHost and HTTP.

This is required for csmith/docker-service-nginx#3

The previous one didn't really work (the way we update files
doesn't trigger the modify event) and broke for newer versions
of Docker (which require a HTTP Host header).

Fixes #5

Closes #6

Define names for everything instead of using the default
compose names.