qt: merge walletstack and walletframe

There were too many levels of indirection here, and the functionality of
walletframe and walletstack can easily be merged. This commit
merges the two which cuts a lot of lines of boilerplate code.

src/qt/walletview.h

@@ -36,7 +36,7 @@ class WalletView : public QStackedWidget
     Q_OBJECT
 
 public:
-    explicit WalletView(QWidget *parent, BitcoinGUI *_gui);
+    explicit WalletView(QWidget *parent);
     ~WalletView();
 
     void setBitcoinGUI(BitcoinGUI *gui);
@@ -64,7 +64,6 @@ private:
     AddressBookPage *addressBookPage;
     AddressBookPage *receiveCoinsPage;
     SendCoinsDialog *sendCoinsPage;
-    SignVerifyMessageDialog *signVerifyMessageDialog;
 
     TransactionView *transactionView;