Update katex

Summary:
Both update ke substate so graphie stuff uses new katex, and update the
katex in perseus. We need to include some extra util files for ke, and
the stylesheets for katex changed.

Test Plan:
Make sure normal math in perseus (inside `$`s) works. Make sure math
inside of graphie (like interactive graph) works also.

Reviewers: alex, alpert

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D3664