If the domain_name entered contains subdomains, e.g. `api.example.com`
then do *not* add an additional `www.api.example.com` route to traefik
If the user enters only the domain `example.com` then add the optional
`www.example.com` Host to the traefik routers.
## Description
Replace Caddy with Traefik
## Rationale
There is some trouble with the Caddy license (https://github.com/pydanny/cookiecutter-django/pull/1282#issuecomment-329617536)
@drdaeman suggested using Traefik (https://github.com/pydanny/cookiecutter-django/pull/1282#issuecomment-353655273) which supports ACME and also plays very nice with Docker.
## Comments
I am currently using the proposed setup on a live site and it working great so far. If this PR is of interest to the maintainers, then I could commit more changes and take care of the documentation. Of course, any suggestions by the more experienced people around here, are welcome!
