Added Manifest for Listener

Added Manifest and Tests for Listener Element in server.xml. Updated the README and added an example for Tomcat 7 Instance with JMX Listener.
Instead of having this block can we have `$class_name` default to `$name`? (see https://github.com/puppetlabs/puppetlabs-tomcat/blob/master/manifests/config/server/host.pp#L34-L38)