This is a GAppLaunchContext subclass meant to replace usage of
GdkAppLaunchContext in gnome-shell.
Launch contexts get created from the MetaStartupNotification as
they are closely related. The messaging underneath depends on
the availability of a X11 display, if there is one we go through
it (and libsn). If there is none, we still create startup sequences
manually for wayland clients.
