Minimize qt windows when using qtwayland platform plugin (xdg-shell support)

Current version of qtwayland and wayland do not support minimization (hide/show window),
but there's a proposal to get this feature using alternate shell xdg.

The xdg-shell protocol is not yet accepted as wayland stable API
but it's good postive feedback since it's already used
or proposed for others toolkits : EFL, GTK+ and Ozone too.

And noticed that it was not in Qt, so I tried to fix this gap.

I've experimenting this on tizen platform which is shipping

• qt5-qtwayland-5.2.95+rc1 (e7a1e121d9cb92e89e53baba81aceedca24f2b94)
• wayland 1.4.0

You can check a demo video (qt-tizen-qtwayland-xdg-shell-20140425-rzr)
of the use case at :

https://www.youtube.com/watch?v=awQHSkO7PKc#

Is anyone interested for testing this, I shared the code in my git branch :

https://qt.gitorious.org/qt/qtwayland-rzr# sandbox/pcoval/for-upstream

Now I guess I should push to the dev branch for reviewing on :
https://codereview.qt-project.org/#dashboard,1003234.

The feature can be disabled at compile time by removing the flag in client.pro
Since xdg-shell is experimental, code fallback to WaylandShell is no xdg

Regards