Add Dockerfile for multi stage builds

[haxorof]

Since Docker CE v17.06 multi stage builds are available which simplifies the process to create smaller images. Today we do it in two stages where releases are published to releases and then packages into container in Docker Hub. Now this can be replaced by this new feature:
https://docs.docker.com/engine/userguide/eng-image/multistage-build/#use-multi-stage-builds

Estimate is that this feature will be available at Docker Hub in July 2017.

Add additional Dockerfile for multi stage builds.