ONOS-895: Group manager implementation

Change-Id: Ie183f722fa39012f8de056961715c325e2388e63
diff --git a/core/api/src/main/java/org/onosproject/net/group/Group.java b/core/api/src/main/java/org/onosproject/net/group/Group.java
index f7fa507..b7872de 100644
--- a/core/api/src/main/java/org/onosproject/net/group/Group.java
+++ b/core/api/src/main/java/org/onosproject/net/group/Group.java
@@ -26,6 +26,10 @@
      */
     public enum GroupState {
         /**
+         * Group create request is queued as group AUDIT is in progress.
+         */
+        WAITING_AUDIT_COMPLETE,
+        /**
          * Group create request is processed by ONOS and not yet
          * received the confirmation from data plane.
          */
@@ -81,4 +85,11 @@
      * @return number of bytes
      */
     long bytes();
+
+    /**
+     * Returns the number of flow rules or other groups reference this group.
+     *
+     * @return number of flow rules or other groups pointing to this group
+     */
+    long referenceCount();
 }