Ability to set the inclusion of header cells to be copied at runtime

[SabreWolf]

For the plugin slick.cellexternalcopymanager located at https://github.com/6pac/6pac.github.io/blob/master/SlickGrid/plugins/slick.cellexternalcopymanager.js please could you create and expose a function to be able to turn on and off the inclusion of the header cells at runtime when copying and pasting. I have included a suggestion for the last few lines of this file below.

    **function setIncludeHeaderWhenCopying(includeHeaderWhenCopying) {
        _options.includeHeaderWhenCopying = includeHeaderWhenCopying;
	}**

    $.extend(this, {
      "init": init,
      "destroy": destroy,
      "clearCopySelection": clearCopySelection,
      "handleKeyDown":handleKeyDown,
      **"setIncludeHeaderWhenCopying":setIncludeHeaderWhenCopying,**
      
      "onCopyCells": new Slick.Event(),
      "onCopyCancelled": new Slick.Event(),
      "onPasteCells": new Slick.Event()
    });
  }
})(jQuery);