Draft: Add a dbus daemon
Based on https://gitlab.gnome.org/pesader/gnome-network-displays/-/tree/feat/nd-detached-instance by @pesader
I've done a fair bit of cleanup and hopefully simplified a few things.
What's missing really is a client for the new dbus api in order to test whether the new daemon and stand-alone stream instances actually work as intended.
This change adds a daemon program (in src/daemon) and a
stream instance program (in src/stream) for
stand-alone/detached streams that can be controlled
via the new dbus API that is also added.