fix: import errors van gabe gefixt, teacher en student abstractie weggedaan

backend/src/routes/learning-objects.ts

@@ -1,7 +1,9 @@
 import express from 'express';
 import {
     getAllLearningObjects,
+    getAttachment,
     getLearningObject,
+    getLearningObjectHTML,
 } from '../controllers/learning-objects.js';
 
 import submissionRoutes from './submissions.js';