Adopt JupyterLab as the primary interface

# Summary

Adopt the JupyterLab (JL) interface as the primary interface for AiiDAlab.

# Motivation

The [Jupyter notebook interface is deprecated](https://jupyter-docker-stacks.readthedocs.io/en/latest/index.html#jupyter-notebook-deprecation-notice), which means that switching to the more modern JupyterLab interface is eventually necessary.

The JupyterLab interface implement some of the functions that are currently implemented by the AiiDAlab home app. Thus we expect that adopting the JL interface as the primary interface will improve the user experience and reduce maintenance cost.

# Expected outcome

When a user starts AiiDAlab they will be directed to the JL by default and will find all functions that are currently provided by the AiiDAlab home app.