support rich, secure remote notifications

[n8fr8]

• can we do this through pure client/apps code
• we might need to use a server with Signal-CLI

[n8fr8]

related to #20 which might be more viable

[n8fr8]

• We need to support some kind of rich media remote notification to show alert event photos, audio
• Can we just do email?
• XMPP+OMEMO supports attachments, secure data

[n8fr8]

This library looks good for background email sending: https://github.com/yesidlazaro/GmailBackground

[n8fr8]

I think that the Onion/HS is definitely the way to go here, but I do want to add the ability to sync via onion between two PhoneyPot apps. This isn't hard, and it means you can essentially "pair" two phoneypots, with one polling the other at a configurable interval, to synchronize any events that are detected.

We will still support the onion web interface, as well, for accessing from Tor Browser Desktop, Onion Browser iOS, etc.

Also, will be adding a password-based auth mechanism for now, since Authenticated Onions aren't well supported yet on desktop or iOS browsers.

[mrphs]

In case it becomes useful and you probably know this, but there's this TextSecure library and command line tool that INTERLOCK uses to make a minimal Signal client.

[n8fr8]

Interesting - had not seen that! We are using a fork of signal-cli for now, and it seems to be working well.

[9662]

Just linking here my Briar suggestion from #344.

Incidentally, why no XMPP support (yet)? With E2E encryption it offers superior security to signal (choice of and control over server so better metadata protection, no leaking of phone numbers, choice of client, etc.) and is not particularly difficult to implement.