Simpler url page

The URL view had a few problems:

* The graph was an impossible to read mess of dots after some usage.
* No pagination :cry:

I figured the graphs would be much simpler if they only showed averages per day, as you're probably most interested in trends over time which is easier to see when there is less noise.  If Mongo's aggregation had $median I would have used that. For now $avg will have to do.

This change does break existing stored data as the new `meta.request_time` is required for on the URL page.  We probably should have been storing a MongoDate the whole time though.