Dev

There are 3 minor commits inside of this pull request.

(1) Check that $order->shipping_service is non empty before adding it to email.
(2) add filter for new user notification. (jigoshop_new_user_notification)
(3) Added jigoshop_before_billing_fields, jigoshop_before_shipping_fields hooks to checkout page/class.

If you change the hook names, let me know. Thanks!