Add method to obtain historic notifications of scope.

tools.descartes.prisma.core/src/tools/descartes/prisma/core/scopes/AgentScope.java

 package tools.descartes.prisma.core.scopes;
 
+import java.util.Collections;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
@@ -253,6 +254,10 @@ public abstract class AgentScope extends Scope {
 	public void sendNotifications(String notificationType, CDOObject object) {
 	}
 
+	public List<? extends CDOObject> getHistoricNotifications(String exchange) {
+		return Collections.emptyList();
+	}
+
 	protected void sendNotificationMessage(String exchange, String routingKey, ModelNotification notification) {
 		getMessageBus().publishMessage(exchange, routingKey, "", notification);
 	}