Do not create a wl_shell_surface for Qt::CustomWindow

Normal application windows should usually have a wl_shell_surface. But
there are also QWindows which should be used as input panel, lock or
background surface. In this cases they must not be wl_shell_surfaces.

Native wayland API (together with the platform's native interface) can
be used to specify the surface type for that kind of windows.

Change-Id: I0f6c499e60305ab31f545d435e8f25c340d7ac3e
Revert "Read and process Wayland events in separate thread"

This commit causes a regression making QML applications with top level
windows crash.

See https://bugreports.qt-project.org/browse/QTBUG-30156
Revert "Disable desktop settings awareness for now"

We need to enable themes otherwise Hawaii won't be able to
properly work.
Expose window properties to QML

Make window properties available to QML compositors.

Change-Id: Id87a263207dab354fbab4b67bbaaeace37660e9d