[WIP] 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.

> 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 don't think this line is necessary (and the next one probably isn't either).

I copied the autoremove and clean functions from another dockerfile, the idea being (I think) that after removing packages, you also want to remove any packages that were automatically installed as dependencies of those pcakges.

In this RUN command you havan't installed any packages so autoremove should be a noop.

I don't really know what clean does.

Assuming clean is a noop in this context, you can probably just have two RUN commands, one for each apt-get install,

In fact, where I use it below, I think it only saves 0.1 GB (in a ~1GB image).  My own investigations didn't show any wasted space in the file system - I think the scipy stack really does need the whole 1GB - but other's may have better luck.