Fix problem with waitfor keydown or keyup; load MathJax only if used
Fix problem with waitfor keydown or keyup; load MathJax only if used

BruceSherwood/vpython-jupyter,mwcraig/vpython-jupyter,mwcraig/vpython-jupyter,mwcraig/vpython-jupyter,mwcraig/vpython-jupyter,BruceSherwood/vpython-jupyter,BruceSherwood/vpython-jupyter,BruceSherwood/vpython-jupyter