Only an admin or the merchant can edit posts and other DJ Jazzy Jeff stuff

@cgruppioni - please have a look

*Buttons and links only show up if admin, or owner of the post
*Authority is locked down at the controller level
*Product partial updated with seller information, and better flow for readability
*All users can now see categories
*Categories now show the number of items included in them
*Category products now have link to the product
If you're interested, rails has a built in feature that asks if you're sure you want to delete something:

```ruby
<%= button_to "Delete Image", { action: "delete", id: @image.id },
                                method: :delete, data: { confirm: "Are you sure?" } %>
```

Above was taken form http://api.rubyonrails.org/classes/ActionView/Helpers/UrlHelper.html