Resolve "Push subscriptions are stored multiple times in the DB"

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Closes #284 (closed)

src/main/java/nl/tudelft/ewi/queue/controller/NotificationController.java

@@ -108,9 +108,11 @@ public class NotificationController {
 	@RequestMapping(value = "/notifications/subscription", method = RequestMethod.POST)
 	@ResponseStatus(value = HttpStatus.NO_CONTENT)
 	public void subscription(@AuthenticatedUser User user, @RequestBody Subscription subscription) {
-
-		user.setSubscription(subscription);
-
-		userRepository.save(user);
+		Subscription current = user.getSubscription();
+		if (current == null || !(current.getEndpoint().equals(subscription.getEndpoint()))) {
+			user.setSubscription(subscription);
+			userRepository.save(user);
+		}
+		// else: TODO update/refresh?
 	}
 }