Notification support for Consistent datastructures (ConsitentMap and DistributedSet)

Change-Id: If74cdc411c79c42c7643420e6369cf656849bb6a
diff --git a/core/api/src/main/java/org/onosproject/store/service/MapEventListener.java b/core/api/src/main/java/org/onosproject/store/service/MapEventListener.java
new file mode 100644
index 0000000..2856306
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/store/service/MapEventListener.java
@@ -0,0 +1,13 @@
+package org.onosproject.store.service;
+
+/**
+ * Listener to be notified about updates to a ConsitentMap.
+ */
+public interface MapEventListener<K, V> {
+    /**
+     * Reacts to the specified event.
+     *
+     * @param event the event
+     */
+    void event(MapEvent<K, V> event);
+}