This adds a systemd unit file for running the Calls daemon, and adds a
key to the xdg autostart file to instruct gnome-session to ignore
starting when systemd is present. The expectation is that systemd
distros will enable the Calls daemon as a user service and not rely on
xdg autostart / gnome-session for running/managing the service. Systemd
is better at managing services than gnome-session.
Note: it's important to keep the xdg-autostart file around, some distros
(pmOS on openrc, others) don't use systemd and will still need to rely
on the xdg autostart mechanism for starting the Calls daemon.
Co-authored-by: Guido Günther <agx@sigxcpu.org>
