Move ClassLoadingUtil from commons to core-client

The class org.apache.activemq.artemis.utils.ClassLoadingUtil is defined in artemis-commons. In a jboss-modules environment this creates a loop to be able to load classes from another module.

Since this class is only used by the client jars or projects depending on those jars (like server), moving it to artemis-core-client would break the loop and have no consequence on current codebase.