Fix the popups handling.

Use wl_shell_surface_set_popup() instead of wl_shell_surface_set_transient(),
since the latter is not supposed to make the surface follow the transient
parent movements.

Needs Weston master or 1.0.6, otherwise freezes will happen.
To have the best experience you should however use recent weston master.
The popups in QtCompositor are badly placed.

Change-Id: I3c86e5d74503514749840681b4e81c58cd73ca70
Reviewed-by: Andy Nichols <andy.nichols@digia.com>
Reviewed-by: Jan Arne Petersen <jan.petersen@kdab.com>
Generic Wayland platform theme

In 10652f8dd675aa0d12c11597c165831c8ba0b8b4 we disabled desktop
settings awareness because it caused some problems like the GTK+
style being loaded even though it has X11 dependencies.

Unfortunately this prevents the platform theme plugin from being
loaded even for desktops that currently support Wayland.

So the idea is to wrap the generic platform theme around a Wayland
implementation that prevents platform themes for X11 desktop
environments from being loaded without consequences for desktops
supporting Wayland.

When more desktop environments will support Wayland it's worth
reconsidering how the platform theme plugin is loaded.

Change-Id: I0d683bfe491c9421acdb87a8e8f05d99de1ff21f
Reviewed-by: Jan Arne Petersen <jan.petersen@kdab.com>
Reviewed-by: Andy Nichols <andy.nichols@digia.com>