ONOS-4326: Focusing on add/remove cluster member. (WIP).

If reviewing this, please refer to http://tinyurl.com/onos-ui-topo-model

Change-Id: Ic6568074ac768ec828f9103e92caab5e9a06ade6
diff --git a/core/api/src/main/java/org/onosproject/ui/model/topo/UiTopology.java b/core/api/src/main/java/org/onosproject/ui/model/topo/UiTopology.java
index 898c8eb..a8b5b06 100644
--- a/core/api/src/main/java/org/onosproject/ui/model/topo/UiTopology.java
+++ b/core/api/src/main/java/org/onosproject/ui/model/topo/UiTopology.java
@@ -28,6 +28,8 @@
  */
 public class UiTopology extends UiElement {
 
+    private static final String DEFAULT_TOPOLOGY_ID = "TOPOLOGY-0";
+
     private static final Logger log = LoggerFactory.getLogger(UiTopology.class);
 
     private final UiCluster uiCluster = new UiCluster();
@@ -69,6 +71,15 @@
     }
 
     /**
+     * Removes the given cluster member from the topology model.
+     *
+     * @param member cluster member to remove
+     */
+    public void remove(UiClusterMember member) {
+        uiCluster.remove(member);
+    }
+
+    /**
      * Returns the number of members in the cluster.
      *
      * @return number of cluster members
@@ -85,4 +96,9 @@
     public int regionCount() {
         return uiRegions.size();
     }
+
+    @Override
+    public String idAsString() {
+        return DEFAULT_TOPOLOGY_ID;
+    }
 }