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/apps/metrics/topology/src/main/resources/OSGI-INF/blueprint/shell-config.xml b/apps/metrics/topology/src/main/resources/OSGI-INF/blueprint/shell-config.xml
new file mode 100644
index 0000000..c1471da
--- /dev/null
+++ b/apps/metrics/topology/src/main/resources/OSGI-INF/blueprint/shell-config.xml
@@ -0,0 +1,12 @@
+<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0">
+
+  <command-bundle xmlns="http://karaf.apache.org/xmlns/shell/v1.1.0">
+    <command>
+      <action class="org.onlab.onos.metrics.topology.cli.TopologyEventsListCommand"/>
+    </command>
+    <command>
+      <action class="org.onlab.onos.metrics.topology.cli.TopologyEventsMetricsCommand"/>
+    </command>
+  </command-bundle>
+
+</blueprint>