Use Qt signals to process configuration name changes

This change maintains the encapsulation  of the MultiSettings class by
using  a  signal   to  notify  clients  of  changes   to  the  current
configuration name.

Modifications  to   the  MainWindow  class  to   display  the  current
configuration name in the status bar, if it is not "Default", based on
MultiSettings events rather than polling for changes.

git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@7257 ab8295b8-cf94-4d9e-aec4-7959e3be5d79

MultiSettings.hpp

@@ -1,6 +1,7 @@
 #ifndef MULTISETTINGS_HPP__
 #define MULTISETTINGS_HPP__
 
+#include <QObject>
 #include <QVariant>
 
 #include "pimpl_h.hpp"
@@ -59,7 +60,10 @@ class QString;
 //
 
 class MultiSettings
+  : public QObject
 {
+  Q_OBJECT
+
 public:
   explicit MultiSettings ();
   MultiSettings (MultiSettings const&) = delete;
@@ -86,6 +90,9 @@ public:
   // again.
   bool exit ();
 
+  // emitted when the name of the current configuration changes
+  Q_SIGNAL void configurationNameChanged (QString const& name) const;
+
 private:
   class impl;
   pimpl<impl> m_;