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 think this is the best solution.  Can you confirm ```iptest``` does return non-zero exit code on failure?

I agree ```python -c``` is almost as good as ```ipython -c``` and will make our lives much easier.