Ref T246, utility for 1st model set directory

* remove empty enries in directories
* allow to add directory
* detect same directories and avoid duplicates

src/blackmisc/directoryutils.h

@@ -158,6 +158,9 @@ namespace BlackMisc
         static bool isDirExisting(const QDir &dir);
         //! @}
 
+        //! Same existing directories
+        static bool isSameExistingDirectory(const QString &dir1, const QString &dir2);
+
         //! Result of directory comparison
         struct DirComparison
         {