MathJax and KaTeX

[deskinsjt]

Mathjax has closed its cdn, and cdnjs (the one I am currently using) is slightly trickier to get the most recent version automagically. I looked briefly at KaTeX as a replacement. I like that it is lighter and we could do the rendering on the server side if we wanted. There are some issues if we want it done client side, that are nearly completed issues on their github but haven't been pushed to their stable build yet.