Change mathjax to being simply a symlink to /opt/webwork/MathJax.
From the discussion in Vancouver, this was decided to be a better way
to handle MathJax (in a way simpler installation for general users, and
better for developers since you install mathjax once and don't have to
mess with it as you switch webwork versions).  Once people get in sync,
we won't have accidental commits of changes to the mathjax directory.