about.js get sys_info from global namespace.

[Carreau]

1. It might not be defined and we should check for that.
2. it does not always work (like iframing on try.jupyter.org)
3. It make the "about" menu do nothing and it's hard to debug.

[captainsafia]

I think this should be closed or the persistent issues should be split into new, smaller issues.

[Carreau]

Do you want to open sub issues, referencing this and closing this one once the other issues are created?

[captainsafia]

Yep.