on_import add explicit import statement to first Jupyter cell

[FlorianWetschoreck]

In order to remove the possibility that we can forget to copy the explicit import statements to the top of the notebook, it would be great if the explicit import statement (e.g. "import pandas as pd") is added to the first Jupyter cell on_import.

Implementation thoughts:

• in Jupyter Notebook we can simply display() a Javascript snippet which does this action once on_import
• for Jupyter Lab we need to write a custom extension which is triggered on_import

[8080labs]

Closed with the new version 1.0.0