Resolve "Notification asking students for feedback"

Closes #242 (closed), #245 (closed)

This merge request sightly refactors the way notifications are created. The task of creating notifications has been moved to notification service instead of random classes. Also has a new notification been added, the ask for feedback notification for students. If they click on the notification they will be redirected towards the feedback page for that specific request.

Furthemore, it also lets students be notified if a TA is not able to find them.