Add class to ember wrapper div

I have been adding a wrapper for the outlet like @Senthe suggests. Although it’s easy to target the div, it’s certainly not ideal that we don’t have the ability to configure it further. If someone doesn’t already see that it’s a problem - we aren’t going to be able to convince them that it is. : (

templates/application.hbs

<div class='outlet application-outlet'>
  {{outlet}}
</div>