Added markupsafe for requirements

@wedaly @stephensanchez  I needed to add this to make read the docs work.  after this is merged, you can use this as the real URL:  http://edx.readthedocs.org/projects/edx-ora-2/en/latest/

I won't remove the old one (http://edx-tim.readthedocs.org/en/latest/)  for a while.