Adds the SurfaceInterface identified by the surface id we get from
Xwayland. This allows in an easier way to map a Toplevel to a
Wayland surface and will also be useful for Wayland clients.
The WaylandServer is at the moment only used to support starting an
Xwayland. It does not support Wayland clients yet, so don't get
excited.
For Xwayland it's using the trick of creating the Display before the
QApplication is created with manual event dispatching.
