This is required for screensaver inhibition on kde (this might
also be supported on further desktops).

It would appear to make sense to move all screensaver inhibiting
code here into one location, since it should be shared across
the generic unx, and gtk vcl backends - currently we have completely
independent implementations for gtk/gtk3 (which only supports
XSetScreenSaver, and gnome's dbus inhibition), and the generic backend
for all other plugins, which supports XSetScreenSaver, xautolock, DPMS,
but no dbus inhibition.

Change-Id: I9c5af8021b0b49b5c93ed75a7d25e3208d5e9629