Change perseus to match new graphie-to-svg scheme

Summary:
Graphie-to-svg now produces `web+graphie://...` links. This makes
perseus accept these links when rendering.

Test Plan: - Do the same stuff I did in the previous review (D14529) on chrome and IE9

Reviewers: aria

Reviewed By: aria

Differential Revision: https://phabricator.khanacademy.org/D14852