+cdd #16799 Add Distributed Data module

Previously know as [patriknw/akka-data-replication](https://github.com/patriknw/akka-data-replication),
which was originally inspired by [jboner/akka-crdt](https://github.com/jboner/akka-crdt).

The functionality is very similar to akka-data-replication 0.11.

Here is a list of the most important changes:

* The package name changed to `akka.cluster.ddata`
* The extension was renamed to `DistributedData`
* The keys changed from strings to classes with unique identifiers and type information of the data values,
  e.g. `ORSetKey[Int]("set2")`
* The optional read consistency parameter was removed from the `Update` message. If you need to read from
  other replicas before performing the update you have to first send a `Get` message and then continue with
  the ``Update`` when the ``GetSuccess`` is received.
* `BigInt` is used in `GCounter` and `PNCounter` instead of `Long`
* Improvements of java api
* Better documentation

akka-docs/rst/java/code/docs/ddata/DataBot.java

@@ -0,0 +1,95 @@
+/**
+ * Copyright (C) 2015 Typesafe Inc. <http://www.typesafe.com>
+ */
+package docs.ddata;
+
+//#data-bot
+import static java.util.concurrent.TimeUnit.SECONDS;
+
+import scala.concurrent.duration.Duration;
+import scala.concurrent.forkjoin.ThreadLocalRandom;
+
+import akka.actor.AbstractActor;
+import akka.actor.ActorRef;
+import akka.actor.Cancellable;
+import akka.cluster.Cluster;
+import akka.cluster.ddata.DistributedData;
+import akka.cluster.ddata.Key;
+import akka.cluster.ddata.ORSet;
+import akka.cluster.ddata.ORSetKey;
+import akka.cluster.ddata.Replicator;
+import akka.cluster.ddata.Replicator.Changed;
+import akka.cluster.ddata.Replicator.Subscribe;
+import akka.cluster.ddata.Replicator.Update;
+import akka.cluster.ddata.Replicator.UpdateResponse;
+import akka.event.Logging;
+import akka.event.LoggingAdapter;
+import akka.japi.pf.ReceiveBuilder;
+
+public class DataBot extends AbstractActor {
+  
+  private static final String TICK = "tick";
+  
+  private final LoggingAdapter log = Logging.getLogger(context().system(), this);
+
+  private final ActorRef replicator = 
+      DistributedData.get(context().system()).replicator();
+  private final Cluster node = Cluster.get(context().system());
+
+  private final Cancellable tickTask = context().system().scheduler().schedule(
+      Duration.create(5, SECONDS), Duration.create(5, SECONDS), self(), TICK,
+      context().dispatcher(), self());
+
+  private final Key<ORSet<String>> dataKey = ORSetKey.create("key");
+  
+  public DataBot() {
+    receive(ReceiveBuilder.
+      match(String.class, a -> a.equals(TICK), a -> {
+        String s = String.valueOf((char) ThreadLocalRandom.current().nextInt(97, 123));
+        if (ThreadLocalRandom.current().nextBoolean()) {
+          // add
+          log.info("Adding: {}", s);
+          Update<ORSet<String>> update = new Update<>(
+              dataKey, 
+              ORSet.create(), 
+              Replicator.writeLocal(), 
+              curr ->  curr.add(node, s));
+           replicator.tell(update, self());
+        } else {
+          // remove
+          log.info("Removing: {}", s);
+          Update<ORSet<String>> update = new Update<>(
+              dataKey, 
+              ORSet.create(), 
+              Replicator.writeLocal(), 
+              curr ->  curr.remove(node, s));
+          replicator.tell(update, self());
+        }
+      }).
+      match(UpdateResponse.class, r -> {
+       // ignore
+      }).
+      match(Changed.class, c -> c.key().equals(dataKey), c -> {
+        @SuppressWarnings("unchecked")
+        Changed<ORSet<String>> c2 = c;
+        ORSet<String> data = c2.dataValue();
+        log.info("Current elements: {}", data.getElements());
+      }).
+      matchAny(o -> log.info("received unknown message")).build()
+    );
+  }
+
+  
+  @Override
+  public void preStart() {
+    Subscribe<ORSet<String>> subscribe = new Subscribe<>(dataKey, self());
+    replicator.tell(subscribe, ActorRef.noSender());
+  }
+
+  @Override 
+  public void postStop(){
+    tickTask.cancel();
+  }
+
+}
+//#data-bot