code: function createButton(opts) {
      opts = _.defaults(opts || {}, {
          // Aria label for the button
          label: '',
  
          // Icon to show
          icon: '',
  
          // Inner text
          text: '',
  
          // Right or left position
          position: 'left',
  
          // Other class name to add to the button
          className: '',
  
          // Triggered when user click on the button
          onClick: defaultOnClick,
  
          // Button is a dropdown
          dropdown: null,
  
          // Position in the toolbar
          index: null
      });
  
      buttons.push(opts);
      updateButton(opts);
  }
docs: Create a new button in the toolbar