Widgets should save state on restoration

[TK-21st]

Widget session is not saved on restoration making double refresh lose the session.

[TK-21st]

It should also allow user to not restore data if the data is large.
Look into stateDB to see how this can be potentially mitigated.

https://jupyterlab.readthedocs.io/en/latest/extension/extension_points.html#state-database