qt: remove awkward way of setting GUI pages

Selecting the button for a pages was going through bitcoingui->walletframe->walletview->bitcoingui.
Because of this, the actions for the pages had to be exposed on the BitcoinGUI object.

src/qt/walletframe.h

@@ -32,7 +32,7 @@ public:
 
     bool addWallet(const QString& name, WalletModel *walletModel);
     bool setCurrentWallet(const QString& name);
-
+    bool removeWallet(const QString &name);
     void removeAllWallets();
 
     bool handlePaymentRequest(const SendCoinsRecipient& recipient);