Subscription (#7)

* Change update DataPoints by a subscription way

* Remove unused import

* small polish

src/main/java/ch/hevs/isi/web/WebConnector.java

@@ -8,6 +8,8 @@ public class WebConnector implements DataPointListener {
 
     private WebConnector (){
 
+        // Subscribe to the update of DataPoints
+        DataPointListener.subscribeUpdate(this);
     }
 
     public static WebConnector  getMySelf(){