College geocoder

Hey, let me know if you're comfortable with this branch. A couple things:

1. This removes sqlite as the database in preference of PostgreSQL (so we can use hstore) If you need help setting up Postgres locally let me know.

2. Created an Entity model with subclasses (College, Alternative, etc) but most importantly we can add/remove columns at will without having to create migrations (hopefully allows us to iterate quicker)

3. /compare/next chooses a pair of college/alternative and then redirects to /compare/pair_id. This allows people to share links to the same pairs. The logic for generating pairs can be improved later (right now it just randomly selects)

TODO:

What is the status of the comparison UI? We need to decide what data we want to show for colleges, and what to show for alternatives. If we need Chad/Steph to collect more data that we don't have, we need to let them know. Once we know what we want to display, I'll update the models and the import scripts.