Allow Mathjax(Latex) in Student responses

Currently, Latex rendering is only supported for question prompts in ORA2. This
commit introduces Latex rendering in ORA2 peer assessment
view, self assessment view, grade view, and staff-info view. The reason that
this Latex rendering code is inserted directly into ORA2 is that edx-platform,
does not know when to start Latex rendering for ORA2 views that come in via
AJAX. This is a much needed feature for many classes. 
We'll need to make sure the Leaderboard also leverages MathJax when it is enabled for a question.

Rather than calling this in multiple places, you could add a class "latex_response" to each field in the corresponding templates for submissions, peer, self, grading, student training, and leaderboard.  Then, this logic can be moved into oa_server.js render(), and the element can be retrieved by the class for all sections.   

I also noticed that we always use latex, even when it is not configured for a particular problem. If we move to using the classes to retrieve the HTML elements, we could pass the allow_latex boolean into the Django Templates, and only add the "latex_response" class on a problem-by-problem basis. In the Javascript, we could then check to see if there are any matching elements before invoking MathJax.