Consider moving to start-from-session workflow

[wenzeslaus]

The tip in the notebooks about GUI (While executing this notebook, you can launch the GUI in the command line interface...) suggests that you count on a session running in the background. The Windows workflow described in the notebook requires starting a command line which has the session there, so there is the session anyway. Starting another session in the notebook does not make much sense although given how the code behaves it at least somewhat works. ...we may need to rethink the whole thing.