Provide new BusFactory impl allowing for integration customizations of default Bus

We should provide a new version of BusFactory allowing us to customize default beans loaded in default Bus (Manager, Configurer, ...). That would also allow us to avoid shipping all the cxf-extension-*.xml files in jbossws-cxf-client.jar as well as the cxf.xml we also have in that jar with no way of touching it (as the same is in cxf-rt-core.jar and different versions make the CXF behavior unpredictable / dependent on users' classpath configuration).