replace some ugly code in addressbookpage.cpp

- add signals signMessage() and verifyMessage() in addressbookpage.cpp
- connect to them in bitcoingui.cpp to switch to the corresponding tab in the Sign/Verify Message dialog
- make gotoSignMessageTab() and gotoVerifyMessageTab() private slots

src/qt/bitcoingui.h

@@ -132,9 +132,6 @@ public slots:
     void askFee(qint64 nFeeRequired, bool *payFee);
     void handleURI(QString strURI);
 
-    void gotoSignMessageTab(QString addr = "");
-    void gotoVerifyMessageTab(QString addr = "");
-
 private slots:
     /** Switch to overview (home) page */
     void gotoOverviewPage();
@@ -147,6 +144,11 @@ private slots:
     /** Switch to send coins page */
     void gotoSendCoinsPage();
 
+    /** Show Sign/Verify Message dialog and switch to sign message tab */
+    void gotoSignMessageTab(QString addr = "");
+    /** Show Sign/Verify Message dialog and switch to verify message tab */
+    void gotoVerifyMessageTab(QString addr = "");
+
     /** Show configuration dialog */
     void optionsClicked();
     /** Show about dialog */