First working Dockerfile (squashed commits)

Starting to build a DinD Dockerfile. Relevant to #3

Working Dockerfile build. Moving Dockerfile files into contrib. Fixes for production envs

Build process almost complete. Just can't get buildstep to commit in final image

Realised you can't commit Docker images inside DinD because of the /var/lib/docker volume. So need to use --volumes-from

First working version of Dockerfile. Needed to export locale in wrapdocker script. Added to documentation about how best to run.

Add Dockerfile to CHANGELOG