Upgrade of maven plugins (#951)

* Upgrade maven plugins

* Upgrade maven plugins

Some general code cleanup was necessary due to upgrade of PMD and checkstyle.

Also needed to add Junit 4 as a dependency due to Mockito.timout issue found here:
https://github.com/mockito/mockito/issues/152

event-asynchronous/src/main/java/com/iluwatar/event/asynchronous/Event.java

@@ -97,7 +97,7 @@ public class Event implements IEvent, Runnable {
     this.eventListener = null;
   }
 
-  private final void completed() {
+  private void completed() {
     if (eventListener != null) {
       eventListener.completedEventHandler(eventId);
     }