MathJax install should be global

[claresloggett]

MathJax is installed locally to avoid needing to care about IPython Notebook HTTP vs HTTPS issues. It's currently a per-user install, which is wasteful - should be system-wide.

[claresloggett]

Currently not an issue as we're using HTTP only, but this may change depending on CloudMan features.

[madisonkeene]

Aaaaand this one is from 3 years ago - should I close this one too? @claresloggett @nuwang