Show order state changes

Allows an admin to view all state changes to an order from the order edit page. All state changes are already logged in Spree, but there's no way to view them.
Yeah that makes sense. But wouldn't the `StateChangesController` draw a `show` action rather than `index`, as it's showing the state changes for a particular order? The URL would then be `http://somestore.com/admin/state_changes/R12345`