Performance dashboard for one URL route over time

Summary:
I reused url-stats.html, stats for one URL, to show stats for one URL
route, similar to what daily_request_log_urlroute_stats does. This
was made easier by updating data.daily_request_log_urlroute_stats() to
parity with the data.daily_request_log_url_stats() call.

There is also some moving around of functions to put like things near
each other in index.html and data.py.

Test Plan: Tested locally with python main.py -d

Reviewers: csilvers

Reviewed By: csilvers

Differential Revision: http://phabricator.khanacademy.org/D2075