Add a CSS class on required fields labels

This makes it possible to add a ' *' required notifier to labels without
needing a bunch of custom form code in templates.

registripe/forms.py

@@ -62,6 +62,8 @@ class StripeWidgetProxy(widgets.Widget):
 
 class CreditCardForm(forms.Form):
 
+    required_css_class = 'label-required'
+
     def _media(self):
         js = (
             'https://js.stripe.com/v2/',
@@ -142,6 +144,8 @@ class CreditCardForm(forms.Form):
 
 class StripeRefundForm(forms.Form):
 
+    required_css_class = 'label-required'
+
     def __init__(self, *args, **kwargs):
         '''