refs #676, allow 1..n model directories

* adjusted loaders
* changed settings

src/blackmisc/simulation/xplane/xplaneutil.h

@@ -41,9 +41,8 @@ namespace BlackMisc
                 //! In case more then one XPlane version is found, the path to the highest version is used
                 static QString xplaneRootDir();
 
-                //! Directory with models
-                //! \todo needs review
-                static QString xplaneModelDirectory();
+                //! Directories with models
+                static QStringList xplaneModelDirectories();
 
                 //! Exclude directories for models
                 static QStringList xplaneModelExcludeDirectoryPatterns();