Add about dialog to File menu of the connection manager.

Make the contents of the dialog more accurate and include a link to the releasenotes file.

pglab/ConnectionManagerWindow.h

@@ -39,6 +39,8 @@ private slots:
 
     void on_actionConfigureCopy_triggered();
 
+    void on_actionAbout_triggered();
+
 private:
 	Ui::ConnectionManagerWindow *ui;
 	MasterController *m_masterController;