[WIP] Sanitize user data

I believe this sanitizes the user data used directly in templates throughout the Backpack, and removes what seemed to be some dead template code.

We need to do some additional sanitizing [here](https://github.com/stenington/openbadges/blob/89c7333619b2502290c0ecfb627f0d9f38174024/views/backpack.html#L90), for example, where we include JSON-serialized data in script tags.