User can delete posts

Added a button in the posts edit view, allowing the current user to delete their own posts.
Relabeled "edit" links in the index and show pages to "edit or delete." 
I was thinking that it would be a nicer user experience to send users to an allowed location, rather than showing an error, but I'm not sure of how it might affect things like performance and security, etc. Which would be a better choice? @jsteiner