Add nesting level-check to prevent DoSing the MathJax-lib on server
Add nesting level-check to prevent DoSing the MathJax-lib on server

If the level is deeper than 20, user will see the error triangle SVG.

Manual trial/error showed that nesting sqrts to a level bit over 20
started to take a long time for the library even on a fast developer
laptop.

digabi/rich-text-editor,digabi/rich-text-editor,digabi/math-editor,digabi/math-editor,digabi/rich-text-editor