Improve support for JupyterLab

[EugeneLoy]

TBD

Follow up on: https://coq.discourse.group/t/jupyter-kernel-for-coq/256/2

[kevinmehall]

I came across your "auto-rollback" feature while trying to implement something similar for my own kernel. FYI JupyterLab gives each cell a persistent ID and passes cellId and deletedCells metadata on every execute request, accessible by ipykernel in self._parent_header['metadata'].

jupyterlab/jupyterlab#5033
https://github.com/jupytercalpoly/reactivepy

[EugeneLoy]

@kevinmehall Thanks for pointing this out!

Maintaining persistent cell id was a major pain while implementing kernel for vanilla notebook frontend.

I am pretty sure this will help with JupyterLab implementation.