Math - Impliment MathJax

[owlboy]

So, this is the ultimate solution to getting Math working once and for all in a consistent way in Storybook. We probally should have implimented it last year, but I was working hard trying to avoid loading another Javascript library every time a Storybook presentation is used.

So, I feel we should impliment MathJax in the current version of Storybook v3.

If you feel loading this library for every presentation would be a bad practice, then I would request that we do it in a way so it can load optionally based on a sbplus.xml tag.

Something like <storybook mathjax="yes">

https://www.mathjax.org/

[Lin87]

Done!