WIP: Verify requirements page

* WIP implementation of the "verify requirements" page.
* The views return JSON objects with template context; the templates aren't actually rendered yet.
* The tests verify the template context, but this is encapsulated in helper methods.  Once I add template rendering, it should be easy to rewrite those methods to verify the actual content of the page.

@dianakhuang When you get a chance, could you take a look at this?  Looking for feedback on the URL structure and view logic, in particular if I'm missing any states we're going to need.
It's an enumeration; in later versions of this branch, the `MESSAGES