Added additional grammar setting.

I added another setting for a comma delimited list pertaining to additional grammars.
![image](https://cloud.githubusercontent.com/assets/4511972/3923397/1079ce8e-23d3-11e4-94cc-ace53c86a8df.png)

This should be `['HTML'].concat...` The way you're doing it would cause the list to repeat itself anytime the user made config changes after the initial load, and if they removed one from the list it would still exist in `@additonalGramamr` because you're just appending to what's already there.