Allow Mathjax(Latex) in Student responses

Currently, Latex rendering is only supported for question prompts in ORA2. This
commit introduces Latex rendering in ORA2 student response, 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 commit introduces "Preview in Latex" feature which allows students to see
their response rendered in MathJax before submission.

Conflicts:
	openassessment/xblock/static/js/openassessment-lms.min.js
	openassessment/xblock/static/js/openassessment-studio.min.js
fixed tests
Some quick cleanup on Javascript and tests.
Merge pull request #619 from edx/sanchez/mathjax

MathJax Integration
Add updates about image responses, including screen shots
Merge pull request #621 from edx/sylvia/docs/ORA_updates

Add updates about image responses, including screen shots
Fix typo
Merge pull request #622 from edx/sylvia/docs/ORA_updates

Fix typo
Track Changes initial implementation

* Creates "TrackChanges" django model, which ties a (submission_uuid,
  scorer_id) pair to a set of edits suggested by peers for a particular
  submission.
* Adds machinery for on-the-fly installation of the New York Times's ICE
  library for collaborative editing, allowing peer assessors to create
  marked-up versions of submissions, which can then be returned to the
  author as feedback.
* Adds machinery for displaying suggested edits to the creator of a
  submission with their scores and other feedback.
* Configurable within Studio on a per-Assessment basis by including a
  URL to the ICE library as part of the assessment definition.
* For additional details, see:
  https://docs.google.com/document/d/18PITJu133sFpDl_B2GCbo2eb0GODcwVmVsktwPQfVSg/edit?usp=sharing

Co-authored-by: Giulio Gratta <giulio@giuliogratta.com>
Co-authored-by: Steven Burch <stv@stanford.edu>
Co-authored-by: Joe Blaylock <jrbl@jrbl.org>