Add missing querysets.

biscuit/apps/chronos/forms.py

@@ -25,5 +25,7 @@ class LessonSubstitutionForm(forms.ModelForm):
 
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
+        self.fields['lesson_period'].queryset = LessonPeriod.objects.all()
+        self.fields['subject'].queryset = Subject.objects.all()
         self.fields['teachers'].queryset = Person.objects.all()
-        self.fields['room'].queryset = Person.objects.all()
+        self.fields['room'].queryset = Room.objects.all()