update wl shell parent setting code to use clients instead of pixmaps
update wl shell parent setting code to use clients instead of pixmaps

ref T2354

tasn/enlightenment,rvandegrift/e,FlorentRevest/Enlightenment,tizenorg/platform.upstream.enlightenment,rvandegrift/e,tasn/enlightenment,tizenorg/platform.upstream.enlightenment,tasn/enlightenment,rvandegrift/e,tizenorg/platform.upstream.enlightenment,FlorentRevest/Enlightenment,FlorentRevest/Enlightenment