Load the MathJax library and typeset math expressions
any HTML elements to apply MathJax to
This function adds MathJax to the page and typeset the math expressions (if
found) in the content
.... It only needs to be called once in an app
unless the content is rendered after the page is loaded, e.g. via
renderUI(), in which case we have to call it explicitly every
time we write math expressions to the output.