Alerts do not display closing animation or close button

Both Foundation and Bootstrap support closing/dismissing alerts with a close button.

This is more desired behavior than Ember destroying the view itself, although I agree that it needs properly destroyed at some point. Both Foundation and Bootstrap provide events that can be listened to in order to perform this duty, or the alerts could just be destroyed on transition as they do now without much backlash I would think.

Also would allow things like the bootstrap example of buttons embedded within an alert.