Admin can delete or edit any post

https://trello.com/c/pXZllid8/11-as-an-admin-i-can-delete-any-post
A bit more logic than I would like to see in a view. Could you create a view helper (add a method to `app/helpers/application_helper.rb`) to wrap up this logic? Something like:

``` erb
<% if user_can_modify?(post) %>
```

and implement the `user_can_modify?` method in the file described above.