Upgrading metrics to 3.0.1

The only somewhat interesting differences between this and commit: c85718fd7c7a52d359721c47f4a1cb849cc60517

are:
  * that there isn't a notion of AdminEnvironment yet in our fork
  * there was a method Environment.addHealthCheck() which I have removed in favor of environment.getHealthCheckRegistry().register() instead where necessary
Merge pull request #13 from polarbizzle/ISP-143

Upgrading metrics to 3.0.1