Add simulation mode, reading domains from a file

[gelim]

Yo,

Thanks for this nice tool by the way.
Here I'm adding a "simulate" mode to benchmark a bit the external.yaml policy from a static file (for instance with already identified evil domains).
Was trying to modify as less as possible, hence reusing callback() with a fake message dict stuffed with file domains.
But still odd use of the global pbar that I'm required to mute by default to avoid unnecessary output when for instance launching the script with --help or with --simulate when a progress bar does not make sense.

Cheers,

-- Mathieu