Move org.jboss.resteasy.plugins.stats to a separate module

The package org.jboss.resteasy.plugins.stats contains a resource and some related classes that should be moved out of the resteasy-jaxb-provider module, as they really are an utility that a user can decide to deploy on his own. We can reduce the memory footprint of the very common jaxb provider module by moving the stats classes out.