Move auth-related from 'kfet' app to 'kfet.auth'.

kfet/auth/fields.py

@@ -0,0 +1,20 @@
+from django import forms
+from django.contrib.auth.models import Permission
+from django.contrib.contenttypes.models import ContentType
+from django.forms import widgets
+
+
+class KFetPermissionsField(forms.ModelMultipleChoiceField):
+
+    def __init__(self, *args, **kwargs):
+        queryset = Permission.objects.filter(
+            content_type__in=ContentType.objects.filter(app_label="kfet"),
+        )
+        super().__init__(
+            queryset=queryset,
+            widget=widgets.CheckboxSelectMultiple,
+            *args, **kwargs
+        )
+
+    def label_from_instance(self, obj):
+        return obj.name