The functionality to create the connection to a Wayland compositor and
creating a fullscreen surface is moved into wayland_backend.(h|cpp). The
wl_egl_window for the surface is moved into the EglWaylandBackend to have
the actual WaylandBackend free from Egl. This will allow in future to
implement other compositing backends for Wayland which do not use egl.
This means that egl is no longer a build requirement for the wayland
related functionality.
