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/monitoreddatamapper.cpp

@@ -4,9 +4,9 @@
 
 #include "monitoreddatamapper.h"
 
-#include <QWidget>
 #include <QMetaObject>
 #include <QMetaProperty>
+#include <QWidget>
 
 MonitoredDataMapper::MonitoredDataMapper(QObject *parent) :
     QDataWidgetMapper(parent)