add markers to exams (move away from group based to content based permissions)

generic/forms.py

@@ -185,6 +185,17 @@ class ExamAuthorFormMixin(ModelForm):
             widget=FilteredSelectMultiple(verbose_name="Authors", is_stacked=False),
         )
 
+class ExamMarkerFormMixin(ModelForm):
+    class Meta:
+        fields = ["markers"]
+
+    def __init__(self, *args, **kwargs):
+        ModelForm.__init__(self, *args, **kwargs)
+        self.fields["markers"] = ModelMultipleChoiceField(
+            queryset=User.objects.all(),
+            widget=FilteredSelectMultiple(verbose_name="Markers", is_stacked=False),
+        )
+
 
 class ExaminationForm(ModelForm):
     def __init__(self, *args, **kwargs):