Update to Mathjax v4

[Miniland1333]

Test Mathjax v4-alpha and see if there are any compatibility issues.
https://github.com/mathjax/MathJax-src/releases/tag/4.0.0-alpha.1

Version 4 of Mathjax has Line-breaking support, which is what prevented us from upgrading to v3. Once the full release is done in I assume a few months, then we should upgrade to take advantage of the new rendering engine.

Replaces #58

[Miniland1333]

It may also be worthwhile doing a performance comparison between this new version of mathjax and the existing version. The supposed speedup could significantly reduce the batch render times.