Replace calls to metrics.report with calls to logger.info

* Let the metrics transport pull out events it is interested in.
* Add a metricsMiddleware that logs `/sign_in` requests.
* Split off the metrics message filter into its own file to be shared across metrics transports.
Move statsd logging over to use the winston logger bus.

* Listen for various timing and increment messages and do the right thing.
* Add a statsd mock for testing.
* No longer call statsd.*, ship all messages over Winston.
Cleanup the metrics and statsd middlewares.

* Get rid of metrics.report. Update tests to use listened for messages.
* Move logging middleware related functionality to logging/middleware
* formatting
Move statsd filters into their own filter objects.
Add email verification to the metrics that go to kpiggybank.

fixes #3528
Send /wsapi/stage_* events to the KPI backend.

* Add tests in tests/kpi-test.js to ensure both staging and completion events are added to the queue.

fixes #3920