title: Django foreign keys between abstract models
body: <p>My django project has multiple apps with the same model structure.
  In order to avoid copy-pasting of the models file, I wrote a generic_models file that contains abstract models in that structure, and each app has models that inherit from the generic models.</p>
  
  <p>Two of these tables have foreign keys between them.
  I would have liked to define the foreign keys as fields in the abstract models.
  Problem is that a foreign key can't point to an abstract table.</p>
  
  <p>How can I achieve this structure?</p>