Publish Dockerfile

[zzeekk]

Building / setting up SDL with maven works but isn't that easy. It is a lot easier with docker.

SDL should provide a Dockerfile to run the samples.

At first the Dockerfile could be placed in the root directory of the repository, later we might move it into a seperate repository.
The Dockerfile should download the given/latest Spark-Release and SDL-Release. It should not build SDL on it's own.

Note: We should not publish the docker image to a registry like dockerhub, as from a licensing perspective we would then distribute all content. We should not do that as we dont know if the licenses of all components allow us to do this.