Allow setting title in Angular routes.
Prevent problem preview directive from blowing up if student answers are undefined.
Some table sort columns.
Cancel $intervals on $destroy.

Otherwise they keep running when you navigate away (since there isn't a
true page reload with Angular).
Make WebworKService's render method not base64 encode absolute paths.

The render backend supports either passing base64 encoded text or an
absolute path, so avoid mangling absolute paths when they are given to
the AngularJS service to render.
Add ProblemUser view to show a student's current status on a problem.

Incomplete at the moment, just renders the problem currently. Also
includes some service functions needed for this functionality.