refs #887, directories available via CDirectoryUtils/relative paths

* relative cache/settings paths are available relativeFilePath
* directories build in CDirectoryUtils
* directory comparison in CDirectoryUtils
* using CFileUtils to concatenate dir paths
* using URL encoded string for normalized directory (as it can be decoded)

src/blackmisc/datacache.h

@@ -285,6 +285,9 @@ namespace BlackMisc
         //! Method used for implementing session values.
         void sessionValue(const QString &key);
 
+        //! Relative file path in application data directory
+        static const QString relativeFilePath();
+
     private:
         CDataCache();