Remove files from Settings::recentFileList(), if they fail to open. (#268)

- i.e. they no longer exist or have been moved
- update recent file menu in StartupView as Settings change

model/Settings.h

@@ -101,6 +101,7 @@ namespace glabels
 			static int maxRecentFiles();
 			static QStringList recentFileList();
 			static void addToRecentFileList( const QString& filePath );
+			static void removeFromRecentFileList( const QString& filePath );
 
 			static QString recentPrinter();
 			static void setRecentPrinter( const QString& printer );