Refine Tree Panel

As of now we directly override the Ext.tree.AsyncTreeNode rather to do so we can create the FolderNode.js which extend the Ext.tree.AsyncTreeNode

in Tree.js we have used root object to create root node rather to do so we can create separate file called FolderNodeUI.js which is used to create root node as well as folder node.

By using FolderNodeUI.js in future we can enhance the folder node as well(e.g show counter etc.)