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.
Is that really the default behavior? Imho should be false by default - I think of security and stability issues - or am I overly cautious? (you know JMX better than me apparently...)