Add "type" attributes to Topology elements

Add type attributes to Topology elements (ONOS-1575, ONOS-1391)
- add "type" as String attributes
- add "type" to JSON representation

Change-Id: I0ab790cfd18eba17e352780b336e5cd49c6fcb1e
diff --git a/src/main/java/net/onrc/onos/core/topology/web/serializers/LinkEventSerializer.java b/src/main/java/net/onrc/onos/core/topology/web/serializers/LinkEventSerializer.java
index 0678d49..47985b0 100644
--- a/src/main/java/net/onrc/onos/core/topology/web/serializers/LinkEventSerializer.java
+++ b/src/main/java/net/onrc/onos/core/topology/web/serializers/LinkEventSerializer.java
@@ -1,6 +1,8 @@
 package net.onrc.onos.core.topology.web.serializers;
 
 import net.onrc.onos.core.topology.LinkEvent;
+import net.onrc.onos.core.topology.TopologyElement;
+
 import org.codehaus.jackson.JsonGenerator;
 import org.codehaus.jackson.map.SerializerProvider;
 import org.codehaus.jackson.map.ser.std.SerializerBase;
@@ -40,6 +42,7 @@
         //
 
         jsonGenerator.writeStartObject();
+        jsonGenerator.writeStringField(TopologyElement.TYPE, linkEvent.getType());
         jsonGenerator.writeObjectField("src", linkEvent.getSrc());
         jsonGenerator.writeObjectField("dst", linkEvent.getDst());
         jsonGenerator.writeEndObject();