use module-less include file style for the sdk example.

This was proposed by Kavindra and actually it is
probably simpler for newbies. The documentation
already talks about this style, so use it.

doc/examples/addressbook-sdk/part6/main.cpp

@@ -1,4 +1,4 @@
-#include <QtGui/QApplication>
+#include <QApplication>
 #include "addressbook.h"
 
 int main(int argc, char *argv[])