Add BeepSend SMS Gateway.
@ametaireau review.
Make sure the smsGateway priority is set.
Add a priority argument to order and handle fallbacks.
Add SMS Gateways tests.
Create a fallback system for SMS backends.
Add a timeout to refresh the provider order.
Merge pull request #95 from mozilla-services/1035668-acision-beepsend-sms-gateway

Bug 1035668 — Add BeepSend SMS Gateway.