* Clear cached name, groupName in Avatar when an ObjectUpdate has new NameValues.
* Some message paths didn't maintain group title, while others did. (Although I don't think that affects this implementation.)
* In the proxy, do send an avatar update for group title changing to empty string.
* ActivateGroup and RequestAgentDataUpdate commands from UI to app to proxy to sim.
* Message back to UI OnAgentDataUpdate, so that we can tell whether a given group of this agent is already active.