Example compile fix with namespaced Qt

This uses the "unneeded #include" approach, as this looks less
ugly than the QT_{BEGIN,END}_NAMESPACE decoration.

Change-Id: I03b6cf3ebf464134fe78ab49cbbad70c0b5fd42a
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

examples/embedded/flickable/flickable.h

@@ -51,9 +51,7 @@
 #ifndef FLICKABLE_H
 #define FLICKABLE_H
 
-class QMouseEvent;
-class QPoint;
-class QWidget;
+#include <QWidget>
 
 class FlickableTicker;
 class FlickablePrivate;