title: Django admin - list_editable - foreign key attribute?
body: <p>Is it possible to make editable <code>ForeignKey</code> attribute in change list?</p>
  
  <p>Every user has it's <code>UserProfile</code> object (<code>OneToOneField</code>). I want admin to be able to modify <code>UserProfile</code> expiry date from <code>User</code> change list. </p>
  
  <p>I can display the <code>expiry</code> in change list:</p>
  
  <pre><code>class UserCustomAdmin(UserAdmin):
      list_display = ['id', 'username','email', 'last_login','userprofile__expiracia']
      # list_editable = ['userprofile__expiracia']
      exclude = ['groups','user_permissions']
      inlines = [UserProfileInline]
      fieldsets = (
          (None, {'fields': ('username', 'password')}),
          (_('Personal info'), {'fields': ('first_name', 'last_name', 'email')}),
          (_('Permissions'), {'fields': ('is_active', 'is_staff', 'is_superuser',
                                         )}),
          (_('Important dates'), {'fields': ('last_login', 'date_joined')}),
      )
  
      def userprofile__expiracia(self,obj):
          return obj.userprofile.expiracia
  </code></pre>
  
  <p>But I can't add <code>userprofile__expiracia</code> to <code>list_editable</code> list. It raises:</p>
  
  <pre><code>&lt;class 'dashboard.admin.UserCustomAdmin'&gt;: (admin.E121) The value of 'list_editable[0]' refers to 'userprofile__expiracia', which is not an attribute of 'auth.User'.
  </code></pre>
  
  <p>How can I make it work?</p>