Improve statsd logging further

- Record timings for each class of status codes separately. Graphite will also
  present a count & rate for each timing, so we can plot those & use them for
  thresholds.

- Use node-txstatsd's new ability to send multiple timings in one packet.
Fix revision table creation

Somehow we were running without a revision table for a while now, with a
fall-back request to the PHP API for each revision request.

This patch fixes the breakage first, better tests in a follow-up.
Merge pull request #61 from gwicke/unbreak_rev_table

Fix revision table creation
Merge pull request #59 from gwicke/statsd_improvements

Improve statsd logging further
Update node-txstatd package dependency