If we try to query before WaylandServer created the KSldApp the service
owner change is never delivered. Thus a delay till we know that the
service is there on Wayland. On X11 the initialization can be done
directly.
To know when the WaylandServer is fully initialized an additional
signal is added to WaylandServer.
It's created together with input, so that the input mechanismn already
has a way to check whether screen is locked.
Effects doesn't hold a member variable any more and instead uses the
singleton instance.
Being able to monitor whether the screen is locked is useful not only
to the effects system but overall in KWin. Thus to make it possible to
use it from more locations as a first step it's moved into dedicated
source files.
