Add User#admin? method.

Fixes #67
Address state is required (and shouldn't be)

Email validation in checkout controller decorator assumes the
`address` state will be the present. Changed to use the first
checkout step via `current_order.checkout_steps.first`.

Fixes #59
spanish locale added

Fixes #58
added error messages to reset password page
Merge branch '1-3-stable' of github.com:radar/spree_auth_devise into 1-3-stable