Base Dockerfile

This begins the process of laying out the base Dockerfiles as discussed on the mailing list and within https://github.com/jupyter/colaboratory/pull/92.

I'm personally going to go with @KesterTong's outline from the colaboratory Dockerfile because I think it matches the setup we want best and is right in line with users+devs on the list.

> 1. IPython library
> 2. IPython + SciPy library (this is just the SciPy stack since IPython is part of the SciPy 1.0 stack)
> 3. IPython server
> 4. IPython + SciPy server

Dependency graph `1->2, 1->3, 2->4`

In the process here I'll be creating each of these as automated builds on the Docker Hub (albeit on the `base_images` branch).
I like the idea behind this, but my tests suggest that ipython -c doesn't return a non-zero exit code when an error occurs in the command.

I couldn't find a way to get IPython to return an exit code, but you might know a way.  Otherwise there are more complex solutions, which would probably be easiest implemented in a separate shell script.