Update the logos for the demo links

At the moment the JupyterLab shows the Jupyter logo, and the Notebook demo shows the Python logo.


This was briefly mentioned at the weekly JupyterLab meeting last week (https://github.com/jupyterlab/team-compass/issues/135#issuecomment-1063441401)

Maybe we should update the logos to the following?

**JupyterLab**

This one doesn't seem to be official, but is used for the GitHub organization:


or


**Jupyter Notebook**


or


Here is what it could look like:


cc @afshin who brought that point