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/transactionfilterproxy.cpp

@@ -6,10 +6,10 @@
 
 #include "transactiontablemodel.h"
 
-#include <QDateTime>
-
 #include <cstdlib>
 
+#include <QDateTime>
+
 // Earliest date that can be represented (far in the past)
 const QDateTime TransactionFilterProxy::MIN_DATE = QDateTime::fromTime_t(0);
 // Last date that can be represented (far in the future)