Allow MFA factors to provide more guidance text on create workflows
SMS will have these guidance messages:
- "Administrator: you haven't configured any mailer which can send SMS, like Twilio."
- "Administrator: SMS is weak."
- "User: you haven't configured a contact number."
Reviewed By: amckinley
Maniphest Tasks: T920
Differential Revision: https://secure.phabricator.com/D20017