Voice call ground work

Very draft.

Useful links:

• https://gstreamer.freedesktop.org/documentation/rswebrtc/index.html?gi-language=c
• https://github.com/signalapp/ringrtc/issues/55
• https://build.opensuse.org/package/show/network%3Aim%3Asignal/nodejs-signal-ringrtc

Towards &4

Building webrtc is a PITA.

LibWebRTC task list

• Document building patched webrtc in a blog post.
• Fetch built webrtc from some webserver, hard-code SHA384s.
• Allow switching out OpenSSL3 and OpenSSL1 libwebrtc.a based on the sailfish feature flag. whatever we need.
• Allow switching out libwebrtc.a builds that don't match the SHA384, utter a warning. Always error out if it's an old hash; allow invalid hashes with a compile option?

Voice calling task list

• Implement synchronize messages from sync device (sync device takes/declines a call, ...) (seems to work!)
• Implement sync messages from WF to sync devices ("I took the call", mainly, I think)