Provide custom NamespaceHandlerResolver and simplify handlers configuration

Now that we're providing custom namespace handlers (see Spring's NamespaceHandlerSupport) for configuring namespace to default bean mapping, we need to make sure the resolution is reliable. This implies providing a custom namespace handler resolver when parsing the jboss-cxf.xml descriptor.
Moreover, we need to simplify the declaration of namespaces mapping in the spring.handler descriptor in jbossws-cxf-client.jar, as there's overlapping with what's defined in the specific spring.handler descriptors included in CXF component jars.