This ensures that *some* TFA authenticator is always present when
authenticating, even if none is specified in the config.
The TfaAuthenticator does not depend on any configured values, so it can
be created on-demand.
Previously, the path prefix was only set if "windows_paths" was true, regardless
of OS. Now the path prefix is always set on windows and never set on other OSes.
This prevents any conflicts caused by multiple files with the same name.
Conflicts may still arise due to transforms, but that is out of our
control and a user error.
"Crawled" and "Downloaded" are now printed less bright than "Crawling" and
"Downloading" as they're not as important. Explain topics are printed in yellow
to stand out a bit more from the cyan action messages.
