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/transactionview.h

@@ -7,17 +7,17 @@
 
 #include <QWidget>
 
-class WalletModel;
 class TransactionFilterProxy;
+class WalletModel;
 
 QT_BEGIN_NAMESPACE
-class QTableView;
 class QComboBox;
-class QLineEdit;
-class QModelIndex;
-class QMenu;
-class QFrame;
 class QDateTimeEdit;
+class QFrame;
+class QLineEdit;
+class QMenu;
+class QModelIndex;
+class QTableView;
 QT_END_NAMESPACE
 
 /** Widget showing the transaction list for a wallet, including a filter row.