Add support for primary address in user.

Closes #35

Fixes #35

uncloud_pay/serializers.py

@@ -1,6 +1,8 @@
 from django.contrib.auth import get_user_model
 from rest_framework import serializers
 from uncloud_auth.serializers import UserSerializer
+from django.utils.translation import gettext_lazy as _
+
 from .models import *
 
 ###