Event driven architecture refactored.

1. Renamed Message to Event and Event to AbstractEvent
2. Generified Event and Handler
3. Updated EventDispatcher to make unsafe configuration impossible
4. Updated UML diagram accordingly

event-driven-architecture/src/main/java/com/iluwatar/eda/event/UserCreatedEvent.java

@@ -29,7 +29,7 @@ import com.iluwatar.eda.model.User;
  * This class can be extended to contain details about the user has been created. In this example,
  * the entire {@link User} object is passed on as data with the event.
  */
-public class UserCreatedEvent extends Event {
+public class UserCreatedEvent extends AbstractEvent {
 
   private User user;