Bug 1035668 — Add BeepSend SMS Gateway.

https://bugzilla.mozilla.org/show_bug.cgi?id=1035668
Can we standardize the SMS config keys since we will have several of them ?

I am thinking:

SMSBackends: [
 {'name': 'beepSend',
  '...'},
 {'name': 'nexmo',
  ...}
]