Added initial implementation of Topology-related event and
event metrics collector. It can be loaded by one of the following two (new)
features: onos-app-metrics, onos-app-metrics-topology

After loading the module, it subscribes for topology-related events
and keeps the following state:
 (a) The last 10 events
 (b) The timestamp of the last event (ms after epoch) as observed by this
     module
 (c) The rate of the topology events: count, median rate, average rate
     over the last 1, 5 or 15 minutes

The following CLI commands are added:
 * onos:topology-events
   Shows the last 10 topology events

 * onos:topology-events-metrics
   Shows the timestamp of the last event, and the rate of the topology
   events: see (b) and (c) above
diff --git a/utils/misc/pom.xml b/utils/misc/pom.xml
index 5040fb0..d1d3a50 100644
--- a/utils/misc/pom.xml
+++ b/utils/misc/pom.xml
@@ -53,6 +53,11 @@
             <version>3.1.0</version>
         </dependency>
         <dependency>
+            <groupId>io.dropwizard.metrics</groupId>
+            <artifactId>metrics-json</artifactId>
+            <version>3.1.0</version>
+        </dependency>
+        <dependency>
             <groupId>org.apache.felix</groupId>
             <artifactId>org.apache.felix.scr.annotations</artifactId>
         </dependency>