Add content to control messages and style them differently

![screen shot](https://cloud.githubusercontent.com/assets/801452/5558953/f776fb82-8cff-11e4-8362-8ffbab99834a.png)

I added a boolean "control" attribute to the message model. Is that the right way to go about this? I'm wondering if it should instead be an attribute describing what particular type of control message it is.