Needs to implement a dummy switcher item. As the root item of the
switchers are no longer QQuickItem derived it cannot use a QQuickView.
Instead a component gets created and the switcher is just shown on the
primary screen. It's a more appropriate preview now which is not
put into a dialog window.

To make it more realistic (and to be able to dismiss it) the preview
grabs keyboard and mouse and closes itself if escape, return, enter or
space is pressed.

As well clicking outside the preview window closes the preview.