Prepare track selection page for new audit track

This is the platform-side work required to prepare for the new audit track (audit/honor track merge). @wedaly and @dianakhuang, could you please review this?

I also need some design input; I'll be speaking with @marcotuts to get it. I removed the `border-top` property from the CSS since it no longer served a purpose with the honor code dropdown removed. However, there are other issues, and there's nothing keeping us from using the styling used by the experimental branch.
I think this method could be private (prefixed with an underscore).  I also think the docstring could be cleaned up, preferably using the [Napoleon style](http://sphinxcontrib-napoleon.readthedocs.org/en/latest/example_google.html)