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/signverifymessagedialog.cpp

@@ -6,19 +6,18 @@
 #include "ui_signverifymessagedialog.h"
 
 #include "addressbookpage.h"
-#include "base58.h"
 #include "guiutil.h"
-#include "init.h"
-#include "main.h"
-#include "optionsmodel.h"
 #include "walletmodel.h"
-#include "wallet.h"
 
-#include <QClipboard>
+#include "base58.h"
+#include "init.h"
+#include "wallet.h"
 
 #include <string>
 #include <vector>
 
+#include <QClipboard>
+
 SignVerifyMessageDialog::SignVerifyMessageDialog(QWidget *parent) :
     QDialog(parent),
     ui(new Ui::SignVerifyMessageDialog),