This is really intriguing and wasn't happy that the SourceForge file is a Windows exe file, so I looked a little more and found this one at Editor.Javascript.com. This link opens in a new window and it a simple URL from your Moodle to the site. I suspect that if you wanted to, you could download the web page, complete, which includes all the associated files, and post that to your server. As long as you set the correct address, it should work from any Moodle resource where you can set a link, a page, a label, an activity dialogue edit box. How you can link that to the gradebook though... no idea, don't think you can. Screen grabs or copied and pasted code should help solve that problem.