Create Account Settings Controller/Page

- Create account settings controller/view/route
- Move account deletion form to account settings page
initial commit of 2fa settings section
first pass at mobile confirmation refactor

Using user.mobile_number for SMS 2-factor now, rather than profile phone number. Also introduced user.uncofirmed_mobile_number to prevent users from changing mobile number without confirmation.
SMS 2FA should not erase confirmed mobile number
User should redirect back to account settings after setting up 2FA

When 2FA enrollment/mobile confirmation is part of the first time experience, user should be sent to a welcome page. When 2FA enrollment is triggered directly from account settings, user should just get redirected back.
remove old mobile_recoveries table
remove roles_helper.rb

move the roles helper functions into application controller
Clean up account settings controller/view

- remove instance variables
- don't seperate public/private apps in warning
Clean up mobile number error messaage
Report Twilio phone number validation errors
cleanup
Give user guidance on unknown Twilio error
Embarrassing fixes and tests
Merge pull request #455 from 18F/feature/two-factor-settings

Feature/two factor settings