Merge branch 'fix-virtual-room-admin' into 'master'

AKOnline: Fix virtual room admin (url editable again)

See merge request !75

AKOnline/admin.py

 from django.contrib import admin
 
-from AKModel.admin import RoomAdmin
+from AKModel.admin import RoomAdmin, RoomForm
 from AKOnline.models import VirtualRoom
 
 
+class VirtualRoomForm(RoomForm):
+    class Meta(RoomForm.Meta):
+        model = VirtualRoom
+        fields = ['name',
+                  'location',
+                  'url',
+                  'capacity',
+                  'properties',
+                  'event',
+                  ]
+
+
 @admin.register(VirtualRoom)
 class VirtualRoomAdmin(RoomAdmin):
     model = VirtualRoom
+
+    def get_form(self, request, obj=None, change=False, **kwargs):
+        if obj is not None:
+            return VirtualRoomForm
+        return super().get_form(request, obj, change, **kwargs)