Review security of GitHub repository commiters & 2 Factor authentication.

Cf thread on the [Jupyter Mailing list](https://groups.google.com/forum/?utm_medium=email&utm_source=footer#!topic/jupyter/Kxz1JcUzXNM).

It would be a good idea to review:
- Who has commit rights & where
- If they have rights on sensible area try to push for them to enable 2FA.
- Investigate the possibility at making 2FA mandatory through GitHub options.

At the same time, we could likely see if we can clean-up who is in what team, and if developers are still active.

Once this is done, we can also review who has access to non-github resources at the same time:
- readthedocs,
- PyPI
- youtube...

And try to uniformise that; as well as investigate securing the releases processes.