Fixes #68.

On suggestions by yahoe.001 and anm on Transifex.

Closes https://code.briarproject.org/briar/briar-gtk/-/milestones/4

Fixes #12

As of August 7, [a first beta release is available](https://mamot.fr/@KekunPlazas/104648142113069390).

The code to build can now be downloaded from [gnome.org](https://download.gnome.org/sources/libhandy/0.90/).

A [migration guide](https://gnome.pages.gitlab.gnome.org/libhandy/hdy-migrating-0-0-to-1.html) is available, just as [packages for Debian](https://packages.debian.org/bullseye/libhandy-1-0).

Fixes #59.

* Show contact's connection state in list
* Support copying content in messages (#51)
* Fix bug with Briar messages not having text (#56)
* Fix bug with contact's name not showing in private messages (#55)
* Update Briar core to version 1.2.9
* Lots of software tests

Analogous to:
* https://salsa.debian.org/xmpp-team/sms4you/-/commit/6dcf2ccc13d4d2f962fafb96ba9a9ac54ce9fa18.
* https://salsa.debian.org/jbicha/simple-scan