The file_advanced and image_advanced files now use Underscore

Reconfigured the Ajax-based file uploaders to now use `underscore.js` to render the new file uploads on the client side.  The reason is simple: all the attachment data is already there via the uploader, so it doesn't make sense to ping the server for the html.  `Underscore.js` is used to take the date and render it on the client side