Add Dockerfile for BCE image

Just wondering if you might be interested in a Dockerfile for the BCE image.  I think `boot2docker` has gotten much easier to use since you first wrote the SciPy paper, and this is also an easy way deploy these tools (e.g. an RStudio-server instance) on a generic linux server (e.g. digitalocean where having the AMI isn't sufficient and you don't really want to run full virtualization).