AntiEntropy sketch + required Serializer work

Change-Id: Ibac5f4eede6b420202683114c3262e01b7264eff
diff --git a/core/store/dist/src/main/java/org/onlab/onos/store/cluster/messaging/MessageSubject.java b/core/store/dist/src/main/java/org/onlab/onos/store/cluster/messaging/MessageSubject.java
index c7badf2..97cbf1d 100644
--- a/core/store/dist/src/main/java/org/onlab/onos/store/cluster/messaging/MessageSubject.java
+++ b/core/store/dist/src/main/java/org/onlab/onos/store/cluster/messaging/MessageSubject.java
@@ -15,6 +15,12 @@
     LEAVING_MEMBER,
 
     /** Signifies a heart-beat message. */
-    ECHO
+    ECHO,
+
+    /** Anti-Entropy advertisement message. */
+    AE_ADVERTISEMENT,
+
+    /** Anti-Entropy reply message. */
+    AE_REPLY,
 
 }