Improve publish of domain events, see #2202

* Gossip is not exposed in user api
* Better and more events
* Snapshot event sent to new subscriber
* Updated tests
* Periodic publish only for internal stats

akka-cluster/src/multi-jvm/scala/akka/cluster/NodeUpSpec.scala

@@ -60,7 +60,7 @@ abstract class NodeUpSpec
       for (n ← 1 to 20) {
         Thread.sleep(100.millis.dilated.toMillis)
         unexpected.get must be(SortedSet.empty)
-        cluster.latestGossip.members.forall(_.status == MemberStatus.Up) must be(true)
+        cluster.members.forall(_.status == MemberStatus.Up) must be(true)
       }
 
       enterBarrier("after-2")