Use QVideoWidget in the videowidget example.

The videowidget example now uses QVideoWidget instead of a custom
QAbstractVideoSurface, the former being the most straightforward and
fastest way of showing a video in a QWidget.

The old code has been moved to a new example: "customvideosurface".

Change-Id: I15fb4482d0e77bafd24d4cb03316fc8f4ef13c35
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Reviewed-by: Jason Barron <jason.barron@digia.com>

examples/examples.pro

@@ -14,7 +14,8 @@ SUBDIRS += audiodecoder
         audiooutput \
         videographicsitem \
         videowidget \
-        player
+        player \
+        customvideosurface
 
     QT += widgets
 }