Added a new module: ONOS intent metrics application

It can be used as an Intent-related event and event metrics collector.
It can be loaded by one of the following two (new) features:
     onos-app-metrics, onos-app-metrics-intent

After loading the module, it subscribes for intent-related events
and keeps the following state:
 (a) The last 100 events
 (b) The timestamp of the last event (ms after epoch) as observed by this
     module for each event type: SUBMITTED, INSTALLED, WITHDRAWN.
     The missing event type is the equivalent of "Withdraw Requested"
 (c) The rate of each intent event type: count, median rate, average rate
      over the last 1, 5 or 15 minutes

The following CLI commands are added:
 * onos:intents-events
   Shows the last 100 intent events
 * onos:intents-events-metrics
   Shows the timestamp of the last event (ms after epoch) as observed by
   this module for each event type, and the rate of the topology
   events (for each event type): see (b) and (c) above

Change-Id: I9f23e9086bbd433b8f24283539abdeb97e199e2e
diff --git a/features/features.xml b/features/features.xml
index e6c4beb..e363094 100644
--- a/features/features.xml
+++ b/features/features.xml
@@ -199,9 +199,16 @@
 
     <feature name="onos-app-metrics" version="1.0.0"
              description="ONOS metrics applications">
+        <feature>onos-app-metrics-intent</feature>
         <feature>onos-app-metrics-topology</feature>
     </feature>
 
+    <feature name="onos-app-metrics-intent" version="1.0.0"
+             description="ONOS intent metrics application">
+        <feature>onos-api</feature>
+        <bundle>mvn:org.onlab.onos/onos-app-metrics-intent/1.0.0-SNAPSHOT</bundle>
+    </feature>
+
     <feature name="onos-app-metrics-topology" version="1.0.0"
              description="ONOS topology metrics application">
         <feature>onos-api</feature>