Support to unlock screen with U2F device only
Allow to configure the lock screen independent of the login screen (i.e. treat the first login after reboot different from locking the screen by the user or timeout).
The desired behavior is:
- When I log in after a reboot, the login screen should ask for my password with optional two factor authentication (2FA). This should also unlock the keyring.
- For the lock screens, the password should be optional (i.e. it should be accepted also, for example when the U2F device is lost) but in general, unlocking via U2F should be possible without a password (just like you lock your car / house).