Add comment/uncomment function to groovy-console edit menu

Comment or uncomment selected script simply by pressing Ctrl (Command) + /.

![screen shot 2013-11-24 at 6 23 34 pm](https://f.cloud.github.com/assets/2078653/1609891/8369be2e-555f-11e3-97c0-eb0f6f8547f2.png)