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

...g

TNL-823
@waheedahmed @mlkwaqas @adampalay 
@andy-armstrong You are right about that requireJS is not being used in LMS that's why I added try-catch block. Since display method inside updatePage method uses mathjax that's why I added a separate dependency here to be on safe side (like if mathjax not loaded first time with xblock_wrapper for some reason then loading this file will try again to load mathjax) so this change is not necessary.