Migrate away from YUI2 treeview

in YUI3 TreeView has become part of gallery. Update filepicker/filemanager/filebrowser to use YUI3 gallery TreeView

Please note that filemanager.css uses YUI2 class names for treeview to overwrite behaviour

There are several issues with YUI2 TreeView:
1. Empty folder (when expanded) is displayed as a leaf
2. I did not find the way to subscribe to right mouse click
3. I was forced to include in files/renderer.php (function fm_js_template_listfilename) code
<a class="fp-contextmenu" href="#" onclick="return false;">
because Event.preventDefault does not actually prevent following href (and href is needed for keyboard Tab navigation)

$ git grep MDL-32736

files/renderer.php:     * @todo MDL-32736 remove onclick="return false;"

lib/form/filemanager.js:                    // TODO MDL-32736 e is not an event here but an object with properties 'event' and 'node'

repository/filepicker.js:            // TODO MDL-32736 use YUI3 gallery TreeView

repository/filepicker.js:            // TODO MDL-32736 support right click

repository/filepicker.js:                    // TODO MDL-32736 e is not an event here but an object with properties 'event' and 'node'