Relation to Thebe

The behavior of the dashboard server is similar to that of Thebe, but with some key technical differences:

• The notebook code is visible only in the NodeJS application backend.
• The NodeJS backend is the only actor that can send notebook code to a kernel for execution.
• The browser client can only send [Jupyter comm messages](http://jupyter-client.readthedocs.org/ en/latest/messaging.html#opening-a-comm) to kernels (not arbitrary code).
• The application uses various JupyterLab components such as [jupyter-js-services](https://github .com/jupyter/jupyter-js-services) and [jupyter-js-widgets](https://github.com/ipython/ipywidgets/ tree/master/jupyter-js-widgets).