Dependencies for Binder instance

[cameron-toy]

The binder currently doesn't allow viewing ipywidgets or running any of the cells in the demo. I think ipywidgets should be installed at a minimum, and probably enough data science libraries to run the census notebook.

[Zsailer]

You'll need the following dependencies for your current demo notebooks:

• numpy
• matplotlib
• datashader
• pandas
• ipywidgets
• dask