Move Metrics to com.codahale namespace.

This should allow for an easier upgrade path by reducing Maven and classpath conflicts.

Still keeping licensing and copyright info.
Add gauge for pending jobs in InstrumentedQueuedThreadPool.
Added metrics-jetty9 w/ InstrumentedConnector.
Added InstrumentedQueuedThreadPool.
Added InstrumentedHandler.
Upgraded to Jetty 8.1.10.
Fix Maven packaging for metrics-jetty9.
Add YourKit links.
[maven-release-plugin] prepare release v3.0.0-BETA2
[maven-release-plugin] prepare for next development iteration