Adds a Dockerfile for docker build of coLaboratory

Adds a Dockerfile to build a docker image for coLaboratory.  This image is designed to run on a server that users connect to through ssh using port forwarding.  It is not intended to act as a web server, as there is no authentication done by the kernel.
So far I had used a dockerfile that wasn't part of this project, and I was just committing it here, so I hadn't thought of this possibility.