title: Replace "this field is required" message in django admin
body: <p>is there a way to replace the default error message in django admin. I'm using custom widget so I have the form and I was wondering is there something like:<br>
      <code>field_1 = forms.Charfield(widget=X, error_messge='y')</code></p>
  
  <p>I already tried to add claen_field_1 method but it looks that it is not called when the field is empty. Any ideas will be appreciated</p>