Revert "Remove extension whitelist, as further heroku debugging effort."
Revert "Remove extension whitelist, as further heroku debugging effort."

This reverts commit e40d89c3602292230ec43c2b2af29f8d1a70c9cc.

elizabrock/coursewareofthefuture,elizabrock/coursewareofthefuture,elizabrock/coursewareofthefuture