Merge branch 'performance' into 'development'

Send push notifications async

See merge request EIP/queue!34

src/main/java/nl/tudelft/ewi/queue/service/NotificationService.java

@@ -30,7 +30,7 @@ public class NotificationService {
 
         if (null != subscription) {
             try {
-                pushService.send(notificationFactory.fromSubscription(subscription, notification.toJSON().getBytes()));
+                pushService.sendAsync(notificationFactory.fromSubscription(subscription, notification.toJSON().getBytes()));
             } catch (Exception e ) {
                 e.printStackTrace();
             }