callback = function() {
                    if ( ++loaded == arr.length && typeof complete == 'function' ) {
                        complete.call( self );
                    }
                }
Lazy-loads thumbnails.
        You can call this method to load lazy thumbnails at run time

        @param {Array|Number} index Index or array of indexes of thumbnails to be loaded
        @param {Function} complete Callback that is called when all lazy thumbnails have been loaded

        @returns Instance