Fix user account menu to display translations for order state

When the order state is "canceled" a warning is displayed because there is no `en.spree.canceled` translation. This change brings the order state translation closer inline with the payment and shipment state translations (although perhaps it should be named "order_states" and not "order_state", but that's probably a separate PR).

One other small change is to use `String#titleize` on the 3 statuses so that they are displayed consistently.

Fixes #133