remove mathjax form main xmodule requirement and add it on problem addin...

...g

TNL-823
@waheedahmed @mlkwaqas @adampalay 
Why the dependency on JQuery?

If we go this approach, a big comment is needed here explaining what is going on. 

What does the user see if MathJax is needed? Since this is in document ready, will there be an additional delay for the text is rendered (does it render in a different font and then re-render)?