Plotly breaks MathJax in HTML outputs

[atx]

Using Plot.ly plots and MathJax at the same time leads to MathJax not being rendered. See this plot.ly issue for reference. Can be fixed by adding

```julia; echo=false; results="html"
println("<script>window.PlotlyConfig = {MathJaxConfig: 'local'}</script>")
``` `

Somewhere at the start of the document.

Not sure if it's a good idea to just hard code this to the template or have some smarter logic.