title: Add parent field in django admin forms
body: <p>Here are my two models:</p>
  
  <pre><code>class Provider(models.Model):
      name = models.CharField(max_length=75, null=True, blank=True)
      code = models.CharField(max_length=15)
      provider_parent = models.ForeignKey('self', null=True, blank=True)
      accounts = models.ManyToManyField('Account', blank=True)
      data_types = models.ManyToManyField('DataType', blank=True,
                                          through='ProviderDataType')
  
  class Account(models.Model):
      name = models.CharField(max_length=75, unique=True)
      prefixes = models.ManyToManyField('AccountPrefix', blank=True)
  </code></pre>
  
  <p>Here is my admin.py</p>
  
  <pre><code>class ProviderAdmin(admin.ModelAdmin):
      list_display = ('code', '__unicode__')
  
  class AccountAdmin(admin.ModelAdmin):
      list_display = ('__unicode__')
  
  
  admin.site.register(Provider, ProviderAdmin)
  admin.site.register(Account, AccountAdmin)
  </code></pre>
  
  <p>I was wondering if it is possible to have a selection of the parent provider when I try to add or update my account model and upon saving it. The Parent model has already set the account on its manytomany field</p>