Add notebook automated testing

[cisaacstern]

As noted in #32 (comment), we currently do not run the notebooks automatically, either at website build time or as part of our CI testing. We should do that eventually to ensure reproducibility, but it will require, at minimum:

• Resolving Clarify dependency "story" and installation procedure #25 to ensure we know what dependencies are required for each notebook
• Having a smaller subset of data available, as we don't want to pull a large amount of data on every automated run. I believe this will be resolved as part of Add quick start guide to README #22.