Add a Tour of Notebook v7

[jtpio]

Looks like jupyterlab-tour is not supported yet in RetroLab with the plugin failing to activate:

[jtpio]

JupyterLab Tour should now work with RetroLab (fixed in jupyterlab/retrolab#187)

So we could start by adding a simple tour using the settings system, as documented in https://github.com/jupyterlab-contrib/jupyterlab-tour#how-to-add-a-tour-with-advanced-settings