Update khan-exercises based on the current webapp repo.

Summary:
I did this by running local-only/update_local.sh.  I had to update
update_local a bit first, to account for changes to compress.py since
the last time it was run.

Test Plan:
Ran
   python -mSimpleHTTPServer
and visited
   http://localhost:8000/exercises/absolute_value.html
and everything looked ok still...

Reviewers: eater, alpert

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D3949