title: Django - Add an extra field to an inline form in admin interface
body: <p>Suppose I have the following in <code>admin.py</code>:</p>
  
  <pre><code>class ImageInline(admin.TabularInline):
      model = Image
  
  class ObjectAdmin(admin.ModelAdmin):
      inlines = [ ImageInline, ]
  </code></pre>
  
  <p>How do I add an extra field to <code>ImageInline</code> that is not a field in <code>Image</code> model?</p>