HTTP-only configuration in dockerfy image

The httpd-webdav-dockerfy image should provide options to start the WebDAV server on HTTP without requiring HTTPS.

There are several benefits:

Easier to get started: Users can try out a WebDAV server without having to set-up CA-signed or self-signed certificates.
Tests: Easier to set-up. Also the pytest webdav_suite does not yet support HTTPS servers (see docker-basics#10 (closed)).
Terminating TLS at load balancers in front of the WebDAV container: The container communicates with the load balancer over HTTP.