Get clever with statsd middleware buckets.

For parameterized routes like `/object/:id` or `/image/:name.png`
the corresponding buckets would look something like `object._id` and
`image._name_png` respectively. This avoids having lots of buckets
with a single hit each in our api endpoints.

Paths *not handled* by the router, or handled by a route defined with
a regex will get bucketed by the requested path.
Make sure statsd parameterized route bucketing handles multiple params