Added tracking of query strings for pageviews
Added 'most recent sessions' to dashboard
Added page to view visited URLs for a given session
track response status codes in Pageview

and show them in the dashboard
models should not be editable through the admin interface
use datetime objects with timezones in queries
pick better defaults for start and end dates
Merge branches 'status-codes', 'readonly-models', 'use-timezones' and 'start-date-fix'