Don't create wl_shell_surface if BypassWinowManagerHint is set

Custom window types might want to set BypassWinowManagerHint and use
the native Wayland API together with the platform native interface.
In this case wl_shell_surface won't be used.

Change-Id: I66d50fc89901e4ff513b8979d08d7ad7d37f817e
Reviewed-by: Jørgen Lind <jorgen.lind@digia.com>