Add browse page

A few components here:

- the actual browse page
- a new model to contain a summary for each address, which is viewed on the browse page
- a script to populate the db with the above summaries (probably run once/day by cron job in production)
- tests!
Hmm. I think querying against that would be cleaner in some regards, but let's go with this and refactor (significantly) later if necessary.