Detect chrome, warn if other browsers

* Chrome: same as now
* Safari: ![screen shot 2014-08-04 at 11 38 56 pm](https://cloud.githubusercontent.com/assets/526415/3807679/3b39f3de-1c6b-11e4-9765-3f95084a2488.png)
* Firefox: ![screen shot 2014-08-04 at 11 38 47 pm](https://cloud.githubusercontent.com/assets/526415/3807682/434c8f32-1c6b-11e4-9b21-74409779aba2.png)


class: `alert alert-warning` instead of jumbotron and custom color