Feature: StatsD integration

This adds basic integration with [StatsD](https://github.com/etsy/statsd/). Currently only workers and query execution minimal metrics reported. In the future we will report metrics for everything (maybe even including [Bucky](github.hubspot.com/bucky/?h) integration).

I considered wrapping the StatsD client with some Metrics class, which will first aggregate metrics in-process and only if StatsD enabled will report there. But eventually realized that this will be too much work at the moment, which might not worth it. StatsD reporting has very low overhead, so users who don't have StatsD server will just send it to localhost.

An alternative can be to submit a pull request to the `statsd` lib to have a flag, which disables reporting.