Add metrics service (with logging one simple metric)

[melinath]

Currently we only have access to metrics that heroku auto-generates. We need access to more granular data in order to tell what's happening with our application. There seem to be a few options that we could choose from:

• Librato
  • This uses a non-standard format and the documentation does not look great.
• HostedGraphite
  • StatsD
  • A little pricier than datadog, and doesn't provide a good python interface
• Datadog
  • Basically statsd
  • Pretty good documentation
  • Charges by the "host" which we don't really care about, but has a bit of a workaround for that for heroku. They say your "host count" will equal your dyno count.

I am most familiar with Datadog, so would be inclined to give them a shot, then switch to a different service if we have problems with them. Worst case would be that we host our own Graphite server somewhere, since the statsd format is pretty standard.

As a first step, we could start measuring total request time by view.