[Wayland] QMenus created without a parent, but later given one remain top level windows

It seems that if a QWidget is created as a top level widget, then currently thats how the compositor will treat it. This means in weston that if you create a menu this way:

    QMenu *fileMenu = menuBar()->addMenu("File");

Menu's work as expected
However if you create a menu this way:

    QMenu *fileMenu = new QMenu("File");
    menuBar()->addMenu(fileMenu);

Then the compositor will give each menu a random position on the desktop.

We need to make sure to change the wl_shell_surface from a top-level to a transient or popup as appropriate.