Started fleshing out the UI topo model classes.
If reviewing this, please refer to http://tinyurl.com/onos-ui-topo-model

Change-Id: I4738392bec1a89c37dff15eff6fe04d66fcabd95
diff --git a/core/api/src/main/java/org/onosproject/ui/model/topo/UiHost.java b/core/api/src/main/java/org/onosproject/ui/model/topo/UiHost.java
index cd80701..933e469 100644
--- a/core/api/src/main/java/org/onosproject/ui/model/topo/UiHost.java
+++ b/core/api/src/main/java/org/onosproject/ui/model/topo/UiHost.java
@@ -16,8 +16,17 @@
 
 package org.onosproject.ui.model.topo;
 
+import org.onosproject.net.Host;
+
 /**
  * Represents an end-station host.
  */
 public class UiHost extends UiNode {
+
+    private Host host;
+
+    @Override
+    protected void destroy() {
+        host = null;
+    }
 }