Add sorting function for classes (issue #233)

biscuit/apps/untis/api.py

@@ -154,6 +154,8 @@ def format_classes(classes):
     """
     classes_as_dict = {}
 
+    classes = sorted(classes, key=lambda class_: class_.name)
+
     for _class in classes:
         step = _class.name[:-1]
         part = _class.name[-1:]