Add a small systemd user target modelled on miracle-wm-session.target.
It binds to graphical-session.target and orders after
graphical-session-pre.target, so systemd user services declaring
WantedBy=graphical-session.target (panels, portals, notification
daemons, ...) start and stop in sync with a labwc session.
Installed into $systemduserunitdir when the systemd dependency is
available at configure time; on systems without systemd the install
is skipped and labwc's runtime activation of the target fails
gracefully.
The GTK xdg-portal implementation, which is used as
the default behind the wlr xdg-portal implementation,
exposes the Inhibit interface even on a non-Gnome
session. Unfortunately this D-BUS interface does not
work on labwc.
By explicitly disabling this interface, firefox and may be
other applications are not tricked into using the
xdg-portal interface but use the Wayland IdleInhibit
protocol instead which labwc supports.
A .desktop file was previously added for the labwc session, this adds a
badge for it where it is supported. The .desktop files and the badges
are also moved to `data/`.
Ref: #36, 9fa783e, labwc/labwc-artwork#7
