title: Using two models on the same Admin page
body: <p>I'd been searching two days how to make it, and the other question I found are not my problem.
  I have 3 models:</p>
  
  <pre><code>class ProductBase(models.Model):
      title = models.CharField(max_length=50) # and some code
  class Serie(models.Model):
      #some specific fields
      productbase = models.OneToOneField(ProductBase, on_delete=models.CASCADE)
  class Movie(models.Model):
      #some specific fields
      productbase = models.OneToOneField(ProductBase, on_delete=models.CASCADE)
  </code></pre>
  
  <p>The Admin shows me a Create/Edit Form for the ProductBase Model, one for the Serie Model, and one for the Movie Model. But I want to show a Create/Edit Form for Serie/ProductBase Model, and one for Movie/ProductBase Model, so creating a serie, I create a ProductBase and a Serie Model, and a relations between them. I thoght using Inlines but, that's for de ProductBase and I can't regsiter the ProductBAse two times with different AdminModels and Inlines.
  The other way is breaking the ProductBase in the two models Serie and Movie, but that is a bad design.
  Thanks for your help
  Sorry for my English</p>