Inject `nwbfile` code snippet in python console to ensure it also runs on juypyterlab

[sanjayankur31]

Currently we load nwbfile with the file being looked at. However, it'll be good to insert the command itself in the python console so that the script can then be used elsewhere also, like in the jupyterlab workspace on v2.

[filippomc]

Now the notebook file is always the same, whathever nwb file we open. Maybe we should create one notebook for each nwb file we open?