Example configuration to simplify the user interface

[jtpio]

When embedding JupyterLab in a IFrame, it can make sense to make the overall interface a bit simpler with less UI elements available to the users.

This could be achieved using the disabledExtensions mechanism of JupyterLab:

• setting the list of plugins and / or extensions to disable in a page config file
• running jupyter labextension disable on individual plugins and extensions

This can be documented via examples, after #5. Example plugins to disable:

• file browser
• extension manager
• topbar