Add a button to open the config file in a text editor

src/qt/optionsdialog.h

@@ -47,6 +47,7 @@ private Q_SLOTS:
     /* set OK button state (enabled / disabled) */
     void setOkButtonState(bool fState);
     void on_resetButton_clicked();
+    void on_openBitcoinConfButton_clicked();
     void on_okButton_clicked();
     void on_cancelButton_clicked();