duplicate "date" kind with a prefix

Later sites will switch to it so the "date" kind can be removed as it
will be existing natively in Authentic.

src/authentic2_auth_fedict/__init__.py

@@ -73,6 +73,11 @@ class Plugin(object):
              'deserialize': json.loads,
              'name': 'date',
              'field_class': fields.DateField, },
+            {'label': _('Date'),
+             'serialize': json.dumps,
+             'deserialize': json.loads,
+             'name': 'fedict_date',
+             'field_class': fields.DateField, },
             {'label': _('Street'),
              'serialize': json.dumps,
              'deserialize': json.loads,