Add RequestId, 4x4 logging and metrics

Adds logging of the following headers: `X-Socrata-RequestId` and `X-Socrata-4x4`.
Adds standard codahale metrics logging and graphite reporting for HTTP requests.
Not quite.  There can be (generally are, but it's gated by data size) multiple row updates in a single `RowDataUpdated` log event.  Given an RDU it's easy to find out how many updates are in it, and only slightly more difficult to find out how many inserts/updates/deletes.

Of course DDL log eevnts are a whole other kettle of fish, since they conceptually touch every row.