Better support for parallel regions

- Generally fixes #68
- First attempt to externalize event execution from state machine
  into its own class backed by an interface. This relates to #7
- Change of various places to have better support if execution
  is done in threads.
- Not yet a central place where concurrency can be defines, thus
  currently rely on global taskExecutor bean when can be overridded
  from a default which is SyncTaskExecutor. Futher work for
  that in separate tickets.
- Change tasks sample to use a thread pool.
- Change of concept how initial state/transition is handled, no
  longer handled manually in lifecycle method, thus giving a change
  for initial transition to execute its actions in a multiple threads.

spring-statemachine-samples/tasks/src/test/java/demo/tasks/TasksTests.java

@@ -46,22 +46,22 @@ public class TasksTests {
 
 	@Test
 	public void testRunOnce() throws InterruptedException {
-		listener.reset(3, 0, 0);
+		listener.reset(9, 0, 0);
 		tasks.run();
-		assertThat(listener.stateChangedLatch.await(2, TimeUnit.SECONDS), is(true));
+		assertThat(listener.stateChangedLatch.await(6, TimeUnit.SECONDS), is(true));
 		assertThat(machine.getState().getIds(), contains(States.READY));
 	}
 
 	@Test
 	public void testRunTwice() throws InterruptedException {
-		listener.reset(3, 0, 0);
+		listener.reset(9, 0, 0);
 		tasks.run();
-		assertThat(listener.stateChangedLatch.await(2, TimeUnit.SECONDS), is(true));
+		assertThat(listener.stateChangedLatch.await(6, TimeUnit.SECONDS), is(true));
 		assertThat(machine.getState().getIds(), contains(States.READY));
 
-		listener.reset(3, 0, 0);
+		listener.reset(9, 0, 0);
 		tasks.run();
-		assertThat(listener.stateChangedLatch.await(2, TimeUnit.SECONDS), is(true));
+		assertThat(listener.stateChangedLatch.await(6, TimeUnit.SECONDS), is(true));
 		assertThat(machine.getState().getIds(), contains(States.READY));
 	}
 
@@ -70,19 +70,19 @@ public class TasksTests {
 		listener.reset(11, 0, 0);
 		tasks.fail("T1");
 		tasks.run();
-		assertThat(listener.stateChangedLatch.await(2, TimeUnit.SECONDS), is(true));
+		assertThat(listener.stateChangedLatch.await(6, TimeUnit.SECONDS), is(true));
 		assertThat(listener.stateChangedCount, is(11));
 		assertThat(machine.getState().getIds(), contains(States.READY));
 	}
 
 	@Test
 	public void testFailManualFix() throws InterruptedException {
-		listener.reset(3, 0, 0);
+		listener.reset(9, 0, 0);
 		tasks.fail("T2");
 		tasks.run();
 		tasks.fix("T2");
 		tasks.cont();
-		assertThat(listener.stateChangedLatch.await(2, TimeUnit.SECONDS), is(true));
+		assertThat(listener.stateChangedLatch.await(6, TimeUnit.SECONDS), is(true));
 		assertThat(machine.getState().getIds(), contains(States.READY));
 	}