Change update DataPoints by a subscription way

src/main/java/ch/hevs/isi/db/DatabaseConnector.java

@@ -56,6 +56,9 @@ public class DatabaseConnector implements DataPointListener {
         if (bucket == null){
             bucket = properties.getProperty("BUCKET");
         }
+
+        // Subscribe to the update of DataPoints
+        DataPointListener.subscribeUpdate(this);
     }
 
     /**