Fixed several memory and thread leaks. See #1404

* Dispatchers need Scheduler to be able to shutdown themselves. Stop Scheduler after dispatchers.
* Changed CallingThreadDispatcher global object to Extension, since it holds map of references to mailboxes. Will be GC:ed when system is GC:ed.
* Made testActor lazy, since it is not used in all tests, and it creates CallingThreadDispatcher.
* Activated some java tests that were not running
* Many tests were not stopping created ActorSystems. VERY IMPORTANT TO STOP ActorSystem in tests. Use AkkaSpec as much as possible.
* Used profiler to verify (and find) dangling ActorSystemImpl and threads from dispatchers.
* FutureSpec creates ForkJoinPool threads that are not cleared, but number of threads don't grow so it's not a problem.

akka-actor-tests/src/test/java/akka/util/JavaDuration.java

@@ -7,7 +7,8 @@ import org.junit.Test;
 
 public class JavaDuration {
 
-  @Test void testCreation() {
+  @Test
+  public void testCreation() {
     final Duration fivesec = Duration.create(5, "seconds");
     final Duration threemillis = Duration.parse("3 millis");
     final Duration diff = fivesec.minus(threemillis);