title: Create a hidden field in the admin site
body: <p>How can I create a fully hidden field (input and label) in the admin site?
  I know about the <code>exclude</code> property, but it fully excludes the field from the template, while I need it in the web page, but hidden:  </p>
  
  <pre><code>class OutForm(ModelForm):
      reply_to = forms.ModelChoiceField(queryset=InMessages.objects.all(), widget=forms.HiddenInput)
  </code></pre>
  
  <p>In the admin template I actually can hide a field, but not its label.</p>