JupyterLab is provided side-by-side with Jupyter Classic interface with same process.

Published URL changed:

• jupyterlab-url provides IPv6 URL to JupterLab interface
• jupyter-class-url provides IPv6 URL to the classic UI

Thanks to using only one process, the path in the URL differentiates the style of the interface.

Note: This MR replaces closed !207 (closed)