Changes to reading room scraping code (better domain matching, better redirect handling)

The CIA landing page had no reading room links. This turned out because the reading room code needed some changes. Those changes are below. Namely domains are matched more accurately using second level domains. Also, 302 redirects are handled more gracefully. 

There's also some PEP8 and syntax related clean up. 

This PR fixes: https://github.com/18F/foia-hub/issues/309