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!
`fire_incidents_query` is a SQLAlchemy structure representing the actual query. Calling `.all()` on it fetches the actual results, which is what we want here.