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/test/uritests.cpp

@@ -1,6 +1,7 @@
 #include "uritests.h"
-#include "../guiutil.h"
-#include "../walletmodel.h"
+
+#include "guiutil.h"
+#include "walletmodel.h"
 
 #include <QUrl>