getall command to save emails locally

Hi,

I was looking for a way to automatically keep a local copy of all emails arriving into guerrilla inbox, and added a "getall" command to your python client that allows to do that. Just though that maybe you would be interested in it, too, and would like to merge it into your version.

Cheers.
Should make the existing format_email method in GetEmailCommand reusable and call it from here.