Cleanup code using forward declarations.

Use misc methods of avoiding unnecesary header includes.
Replace int typedefs with int##_t from stdint.h.
Replace PRI64[xdu] with PRI[xdu]64 from inttypes.h.
Normalize QT_VERSION ifs where possible.
Resolve some indirect dependencies as direct ones.
Remove extern declarations from .cpp files.

src/qt/csvmodelwriter.h

@@ -5,8 +5,8 @@
 #ifndef CSVMODELWRITER_H
 #define CSVMODELWRITER_H
 
-#include <QObject>
 #include <QList>
+#include <QObject>
 
 QT_BEGIN_NAMESPACE
 class QAbstractItemModel;