title: django-allauth - Overriding default signup form
body: <p>I'm using this code (in forms.py) for my custom signup form for allauth:</p>
  
  <pre><code>class RegistrationForm(UserCreationForm):
      birth_date = forms.DateField(widget=extras.SelectDateWidget(years=BIRTH_DATE_YEARS))
  
      class Meta:
          model = get_user_model()
          fields = ('username', 'email', 'password1', 'password2', 'first_name', 'last_name', 'gender', 'birth_date', 'city', 'country')
  </code></pre>
  
  <p>I have of course specified <code>ACCOUNT_SIGNUP_FORM_CLASS</code> in settings.py to point to this form and it displays the fields which I've put in it. However, it does not work on submission, even if I put <code>signup</code> method it never gets invoked. I've tried with the <code>save</code> but still it's the same - it raises an error that one of my custom added fields is blank while creating user and saving it to the database.
  So, what's the correct code for achieving this?</p>