Jn cluster split support

With these changes, an event can be triggered every time a new shard is added to the cluster. The event is not triggered on startup when clusters are detected and added (possible by checking if the number of registered service members == 0).

The NewMemberAddedEvent is used to refresh the server cache in ConsistencyMasterSlave (which observes the service for the event). Without this change, servers would replicate from the wrong source after a shard split. A full edge reset would be necessary.