MDL-32083: Filepicker tree view should display folders starting from top
MDL-32083: Filepicker tree view should display folders starting from top

 - path bar is not displayed in tree view mode
 - display (and load) hierarchy of folders above the current - take it from path and load siblings
 - make sure the current folder is remembered when navigating between folders in tree view so it remains when switching to other view mode
 - fix couple of small bugs caused by previous changes in MDL-31901

dilawar/moodle