uploadItem(value) {
            var index = this.getIndexOfItem(value);
            var item = this.queue[index];
            var transport = this.isHTML5 ? '_xhrTransport' : '_iframeTransport';

            item._prepareToUploading();
            if(this.isUploading) return;

            this._onBeforeUploadItem(item);
            if (item.isCancel) return;

            item.isUploading = true;
            this.isUploading = true;
            this[transport](item);
            this._render();
        }
Uploads a item from the queue
@param {FileItem|Number} value