Make comparisons linkable

[mshenfield]

e.g. someone could navigate directly to "highqualitygifs - reactiongifs", or any other valid combination.

This could be tough to configure:

• Get Apache or Flask to return the index page for urls like http://subreddit-algebra.science/neutralpolitics/-/politics
• Update the Flask server to host the API endpoints at /api. They aren't prefixed in development because I'm not sure how to change the prefix for different environments with Flask. In production, the WSGI app is mounted at /api because I wasn't able to figure out how to mount it at root (/) and still serve the index.html from Apache.

On the frontend, it would mean adapting to use the latest version of react-router