Add integrated Metrics support

This is a basic integration of [Metrics](http://metrics.codahale.com) support.  It currently collects and exposes Route and JVM metrics over JMX (install MBean plugin in VisualVM).  Individual controller methods may be annotated with `@Timed` for the integration to collect and report metrics.

This PR will create a merge conflict with #195 since they both implement a `getRoutes()` method for the Router.  Assuming one or the other is merged, I will rebase.
I don't actually think it enables JMX TCP serving so this is likely poorly worded - and poorly named by the Metrics project.

What I believe it does is exposes the metric registry through MBeans which *can* be reported via JMX.  MBeans are also visible from VisualVM/JConsole with a direct process connection - which is how I view them.  I don't believe JmxReporter explicitly starts tcp JMX server - I thought that was a VM level function.

We can certainly disable that flag by default and rename it as needed.  Maybe `metrics.mbeans.enabled` ?