ChangeEvent: Add 'who' and 'when' fields and methods

The 'when' field tells when the event occurred, and 'who' tells which
account performed the action that triggered the event.

Deprecate the existing events' get..() methods in favor of getWho().

Change-Id: I3fdae6c5b76eda8494bf3b5c95ea6bb077690d04

gerrit-server/src/main/java/com/google/gerrit/server/change/PutTopic.java

@@ -131,7 +131,8 @@ public class PutTopic implements RestModifyView<ChangeResource, Input>,
       if (change != null) {
         topicEdited.fire(change,
             ctx.getUser().asIdentifiedUser().getAccount(),
-            oldTopicName);
+            oldTopicName,
+            ctx.getWhen());
       }
     }
   }