- Add a `destroy_user` ability. This didn't exist before, and was implicit in
other abilities (only admins could access the admin area, so only they could
destroy all users; a user can only access their own account page, and so can
destroy only themselves).
- Grant this ability to admins, and when the current user is trying to destroy
themselves. Disallow destroying ghost users in all cases.
- Modify the `Users::DestroyService` to check this ability. Also check it in
views to decide whether or not to show the "Delete User" button.
- Add a short summary of the Ghost User to the bio.
Rather than using a separate `ghost` state. This lets us have the benefits of
both ghost and blocked users (ghost: true, state: blocked) without having to
rewrite a number of queries to include cases for `state: ghost`.
- 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.
