Update demos

Many of the demo scripts in `chaco/examples/demos` are broken, with a variety of failure modes: either the UI fails to start and the script exits with a traceback, or the UI starts but doesn't display anything, or ...

Steps to reproduce:
- Create a fresh Python 2 EDM environment; populate with Chaco and other dependencies (e.g., some of the examples use SciPy).
- Attempt to run a few of the demo scripts.

I was testing on Python 2 (for the purposes of demonstrating Chaco during a training class), but I dare say that the situation is equally bad or worse on Python 3.

It would be good to go through and resurrect as many of these as possible, and to either open issues for those that can't be resurrected without significant work, or perhaps simply delete them.

We might also consider ways to introduce automated tests for at least some of these demos.

The first step would be to systematically go through the existing demos and catalog which ones work, on which versions of Python, and which platforms. That's an easy task, and I've labelled this issue accordingly.