Qt5 compatibility

This commit squashes all the changes in the Qt5 branch
relative to master.

Backward compatibility with Qt4 is retained.

Original authors:

- Philip Kaufmann <phil.kaufmann@t-online.de>
- Jonas Schnelli <jonas.schnelli@include7.ch>

src/qt/qrcodedialog.cpp

@@ -7,7 +7,9 @@
 #include "optionsmodel.h"
 
 #include <QPixmap>
+#if QT_VERSION < 0x050000
 #include <QUrl>
+#endif
 
 #include <qrencode.h>