Migrations shouldn't fail RuboCop checks - especially lint checks, such
as the nested method check. To avoid changing code in existing
migrations, add the magic comment to the top of each of them to skip
that file.
- To hold registrations from U2F devices, and to authenticate them.
- Previously, `User#two_factor_enabled` was aliased to the
`otp_required_for_login` column on `users`.
- This commit changes things a bit:
- `User#two_factor_enabled` is not a method anymore
- `User#two_factor_enabled?` checks both the
`otp_required_for_login` column, as well as `U2fRegistration`s
- Change all instances of `User#two_factor_enabled` to
`User#two_factor_enabled?`
- Add the `u2f` gem, and implement registration/authentication at the
model level.
Sean McGivern