subscriptions: add date_of_birth for new users created in subscription form

subscription/templates/subscription/subscription.jinja

@@ -15,6 +15,7 @@
         <p>{{ form.first_name.errors }}<label for="{{ form.first_name.name }}">{{ form.first_name.label }}</label> {{ form.first_name }}</p>
         <p>{{ form.last_name.errors }}<label for="{{ form.last_name.name }}">{{ form.last_name.label }}</label> {{ form.last_name }}</p>
         <p>{{ form.email.errors }}<label for="{{ form.email.name }}">{{ form.email.label }}</label> {{ form.email }}</p>
+        <p>{{ form.date_of_birth.errors }}<label for="{{ form.date_of_birth.name }}">{{ form.date_of_birth.label}}</label> {{ form.date_of_birth }}</p>
     </div>
     <p>{{ form.subscription_type.errors }}<label for="{{ form.subscription_type.name }}">{{ form.subscription_type.label }}</label> {{ form.subscription_type }}</p>
     <p>{{ form.payment_method.errors }}<label for="{{ form.payment_method.name }}">{{ form.payment_method.label }}</label> {{