Moved the Initialisation of the CommunicationsManager to a ApplicationPlugin.

Also in that plugin it registers the IUserService with all the Scenes (as they are created). So now we can start changing over all uses of IUserService, that currently access it from the CommunicationsManager to accessing it from the Scene.RequestModuleInterface call. 
Once that is done we can move the UserService creation out to its own plugin and remove all references to it from the CommunicationsManager. Then we can take the next CommunicationsManager interface and repeat.

OpenSim/Framework/IScene.cs

@@ -89,6 +89,9 @@ namespace OpenSim.Framework
         T RequestModuleInterface<T>();
         T[] RequestModuleInterfaces<T>();
 
+        void RegisterModuleInterface<M>(M mod);
+        void StackModuleInterface<M>(M mod);
+
         void AddCommand(object module, string command, string shorthelp, string longhelp, CommandDelegate callback);
     }
 }