Better support for long equations

[ludwigschubert]

As discussed on [private repo] track better support for long equations here.

[martinpflaum]

Hi a quick and easy solution is

this will make a horizontal scroll bar visible if the contents of katex-display gets to large - katex-display is created by the katex.render function

.katex is the class for the inline katex stuff .katex-display is the class for display katex stuff

solution is from https://github.com/KaTeX/KaTeX/issues/521