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!
I might have been referring to somewhere else... 'if 'fire_counts' in counts' through 'if 'police_counts' in counts' below is what I now see as DRYable. Also, the address stripping bits.