Make messages look better when located outside of site chrome.

# Changes
 - Make messages look better when located outside of site chrome, by setting a max-width and centering them in the viewport.

# Screenshots
#### Before
![screen shot 2014-09-24 at 10 45 55 am](https://cloud.githubusercontent.com/assets/583202/4389958/8ffee950-43f9-11e4-871e-c5faa35a147f.png)

#### After
![screen shot 2014-09-24 at 10 45 39 am](https://cloud.githubusercontent.com/assets/583202/4389956/8dcba9e8-43f9-11e4-88b2-1ae16ccdc2b2.png)