updated to v6

- code which is about load txt files (this is a gallery!)
* reformated result HTML code (added newline with PHP_EOL)
* reformated javascript code
* "buttons" are changed from id to class
- removed head (root & back links)
* completely rewrite selecting in structure (using local storage)
+ text before path (BEFORE_PATH_TEXT, BEFORE_PATH_LINK)
+ using referrer to select last selected item, not just "back"
* updated help