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/walletmodel.h

@@ -5,19 +5,20 @@
 #ifndef WALLETMODEL_H
 #define WALLETMODEL_H
 
-#include <QObject>
+#include "paymentrequestplus.h"
+#include "walletmodeltransaction.h"
 
 #include "allocators.h" /* for SecureString */
-#include "wallet.h"
-#include "walletmodeltransaction.h"
-#include "paymentrequestplus.h"
 
-class OptionsModel;
+#include <QObject>
+
 class AddressTableModel;
+class OptionsModel;
 class TransactionTableModel;
-class CWallet;
 class WalletModelTransaction;
 
+class CWallet;
+
 QT_BEGIN_NAMESPACE
 class QTimer;
 QT_END_NAMESPACE