Re-enable XDG-Shell, provide XDG-Shell 1.5.0 patch

We re-enable the XDG-Shell build option for Tizen, and provide
a Tizen-specific patch which will make the XDG-Shell code
catch up with Weston 1.5.0.

BUG=XWALK-1382

Signed-off-by: Manuel Bachmann <manuel.bachmann@open.eurogiciel.org>