Refactor: Make NotificationDecoration an Interface

src/notificationsDecorations/DateNotificationDecoration.java

@@ -2,7 +2,7 @@ package notificationsDecorations;
 
 import java.util.Date;
 
-public class DateNotificationDecoration extends NotificationDecoration {
+public class DateNotificationDecoration implements NotificationDecoration {
     private final Date date;
 
     public DateNotificationDecoration(Date date) {

src/notificationsDecorations/NotificationDecoration.java

@@ -1,6 +1,6 @@
 package notificationsDecorations;
 
-public abstract class NotificationDecoration {
+public interface NotificationDecoration {
     /**
      * Each decoration apply a transformation on the content of the Notifications
      * @return the content transformed

src/notificationsDecorations/WatermarkNotificationDecoration.java

@@ -1,6 +1,6 @@
 package notificationsDecorations;
 
-public class WatermarkNotificationDecoration extends NotificationDecoration {
+public class WatermarkNotificationDecoration implements NotificationDecoration {
     private final String waterMark;
 
     public WatermarkNotificationDecoration(String waterMark) {