Show info and error messages from polkit

If there are some reasons for polkit to show messages to user, e.g. in case if fingerprint is enabled, show the message. Examples of how it will be shown:

Fingerprint auth request:

Wrong finger:

Fingerprint request timeout:

The approach is very simple, and I don't hide password field (even though it doesn't accept passwords now, when waiting for fingerprint, and this is not a regression, but existing behaviour).