Add generic "INTERACTION" event type to UsageStatsManager

This will allow for updating a package's last time used
property for packages that are interacted in ways other than
launching their activities (interacting with notifications, etc.)

Change-Id: Ic6f9519f46fa04abd37ea6fc9475bcd9ea721003

tests/UsageStatsTest/src/com/android/tests/usagestats/UsageLogActivity.java

@@ -166,6 +166,9 @@ public class UsageLogActivity extends ListActivity implements Runnable {
                 case UsageEvents.Event.CONFIGURATION_CHANGE:
                     return "Config change";
 
+                case UsageEvents.Event.INTERACTION:
+                    return "Interaction";
+
                 default:
                     return "Unknown: " + eventType;
             }