code: function openFile(themeId, folderName, fileName) {
          if (themeId && folderName && fileName) {
              //if image then display it
              if (folderName === "images") {
                  showImage(themeId, folderName, fileName);
                  return;
              }
  
              var options = {
                  url:getURL("show") + "/" + themeId + "/" + folderName + "/" + fileName,
                  success:function (response) {
                      if (response.status === "error") {
                          util.showErrorFlash(response.message);
                      }
                      else {
                          // if js, css or jade file then show in editor
                          var mode = "scss";
                          if (fileName.indexOf(".js") > -1) {
                              mode = "javascript";
                          }
                          else if (fileName.indexOf(".css") > -1) {
                              mode = "css";
                          }
  
                          initAceEditor(themeId, folderName, fileName, response, mode);
                      }
                  }
              };
              Rocket.ajax(options);
          }
      }
docs: Handler when theme file is activated in tree, calls io to show file content
  @param {Number} themeId
  @param {String} folderName
  @param {String} fileName