narrowed msg callout width

Made width on ```.message-callout``` on sms campaigns to be more narrow so the text can be closer to the arrow.

Note: enforce content restriction to max out at two lines.

![image](https://cloud.githubusercontent.com/assets/1566749/4380571/457d189a-436b-11e4-85d8-7e11e547abf8.png)

Resolves #2738