Need ability to be able to plugin port invokers that can process results from web services

[sfloess]

SalesforceWebServiceUtil has the ability to create proxy ports via the createProxyPort() method. We need to rethink this as well as the PortInvocationHanlder such that we can either extend or plugin functionality that will allow us to process return values and act accordingly. For example if a web service returns some form of struct that contains error codes, we should be able to plugin and process those values.