Remove samples (#22288)

Add code, that was used for documentation to the appropriate projects
or akka-docs.

akka-docs/rst/java/code/docs/cluster/FactorialBackend.java

@@ -0,0 +1,47 @@
+package docs.cluster;
+
+import java.math.BigInteger;
+import java.util.concurrent.Callable;
+import scala.concurrent.Future;
+import akka.actor.UntypedActor;
+import akka.dispatch.Mapper;
+import static akka.dispatch.Futures.future;
+import static akka.pattern.Patterns.pipe;
+
+//#backend
+public class FactorialBackend extends UntypedActor {
+
+  @Override
+  public void onReceive(Object message) {
+    if (message instanceof Integer) {
+      final Integer n = (Integer) message;
+      Future<BigInteger> f = future(new Callable<BigInteger>() {
+        public BigInteger call() {
+          return factorial(n);
+        }
+      }, getContext().dispatcher());
+
+      Future<FactorialResult> result = f.map(
+          new Mapper<BigInteger, FactorialResult>() {
+            public FactorialResult apply(BigInteger factorial) {
+              return new FactorialResult(n, factorial);
+            }
+          }, getContext().dispatcher());
+
+      pipe(result, getContext().dispatcher()).to(getSender());
+
+    } else {
+      unhandled(message);
+    }
+  }
+
+  BigInteger factorial(int n) {
+    BigInteger acc = BigInteger.ONE;
+    for (int i = 1; i <= n; ++i) {
+      acc = acc.multiply(BigInteger.valueOf(i));
+    }
+    return acc;
+  }
+}
+//#backend
+