Sms verification implement

[moming2k]

I have written part of the Twilio connection , and remaining is save the verification code, checking and add role to user.

[siuying]

i have move SMS and Admin logic to app/models/user/sms_verifiable.rb and app/models/user/adminable.rb.

[siuying]

consider SMS is not part of the first batch of features, we can leave this later

[moming2k]

that's ok , the refactor is nice, good job !