feature: export overview of all contacts

[Meteor0id]

Signal currently never deletes contacts. In fact if you 'remove' a contact you are merely hiding it, but the data is still there. This sucks if you are a journalist who had contact with someone from Navalneys team and your phone gers confiscated and searched in Russia. You think you removed any evidence but it is still there is Signal.

The backuptool could generate a full list, showing which have been hidden and which have not. Such list could help raise awareness of what data lingers in Signal.

Name, profile image, puone number and/or username if available, hidden or not.

--export-contactlist

[Meteor0id]

Duplicate issue due to github glitch