Tune tests, modify web sample, add more logging

- In web sample change other event C to K which brings
  machine back from S2 to S1.
- Add more logging.
- New test sending parallel events.

spring-statemachine-samples/web/src/main/resources/static/index.html

@@ -33,6 +33,7 @@
        				<button ng-click="sendEvent('G')">event G</button>
        				<button ng-click="sendEvent('H')">event H</button>
        				<button ng-click="sendEvent('I')">event I</button>
+       				<button ng-click="sendEvent('K')">event K</button>
        			</div>
 			</div>
 			<div class="row">