Updated SourceCallback class to accept cloning, reversing, and visitors for saving./loading. New mechanism in Source to listen to key triggers for launching SourceCallbacks. Saving and loading in SessionVisitor and SessionCreator.
Translations are in a config xml file in settings directory, and can be directly edited in text by the user. Settings UI allows changing Ports for incoming and outgoing UDP.
Similarly to Node update callbacks, sources now have SourceCallbacks called at the start of each update. Several SourceCallback are implemented to ensure thread safe update of more complex properties (mixing alpha, depth, etc.).
