Created attachment 118495 [details] [review]
Add a systemd user service as a backend for the D-Bus session services

On systems with a systemd user session and a D-Bus user bus that
uses it for activation, this ensures that syncevo-dbus-server ends
up in its own cgroup, instead of being treated as part of dbus.service.

If org._01.pim.contacts and org.syncevolution are activated in quick
succession, it also prevents a race condition that would make one of
the activations fail, similar to
<https://bugs.freedesktop.org/show_bug.cgi?id=53220> in
telepathy-mission-control.