Click handler for export button "download"
@memberof TableExport.prototype
function(event) {
      var target = event.target;
      var object = JSON.parse(Storage.getInstance().getItem(target.getAttribute(this.storageKey))),
        data = object.data,
        filename = object.filename,
        mimeType = object.mimeType,
        fileExtension = object.fileExtension,
        merges = object.merges,
        RTL = object.RTL,
        sheetname = object.sheetname;
      this.export2file(data, mimeType, filename, fileExtension, merges, RTL, sheetname);
    }