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/paymentserver.cpp

@@ -18,7 +18,9 @@
 #include <QLocalServer>
 #include <QLocalSocket>
 #include <QStringList>
+#if QT_VERSION < 0x050000
 #include <QUrl>
+#endif
 
 using namespace boost;