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!
Is it possible to directly filter a query? If so, lines 102 and 103 could be:

fire_incidents_query = db.session.query(FireIncident).filter(FireIncident.alarm_datetime >= two_years_ago))