xdg-shell: upgrade to support current version (weston-1.6.0)

Many inprovements on windows's decorations,

Also handle compositor events
(test: Super+Shift+F , Super+Shift+M)

The protocol file is a raw copy of

Source: http://cgit.freedesktop.org/wayland/weston/plain/protocol/xdg-shell.xml?id=1.6.0

Task-number: QTBUG-38633/related
Change-Id: I667ec52c8a7e34d74b60174a671c89671f841d6b
Reviewed-by: Giulio Camuffo <giulio.camuffo@jollamobile.com>