refactor(backend): Magic values vervangen door constanten.

backend/src/exceptions.ts

@@ -0,0 +1,13 @@
+export class UnauthorizedException extends Error {
+    status = 401;
+    constructor(message: string = "Unauthorized") {
+        super(message);
+    }
+}
+
+export class ForbiddenException extends Error {
+    status = 403;
+    constructor(message: string = "Forbidden") {
+        super(message);
+    }
+}