refactor preferences reset for specs (reduced core test from 9 min to 5 min)
Stringify api_key

By default there is no api key generated. I just managed to break into api on test installation using `?token[]`, one of my favourite CVEs
@radar, please take a look at Mr. Outsider's PR

Fixes #2492
tidy up spree preferences testing support
[api] Added a CheckoutsController
- Allows creation of a new, empty order
- Can transition an order from cart to complete state
- Removed now unneeded address and delivery actions from API's
  OrdersController
[api] Added support for updating an order's payments using CheckoutsController
move rabl configure into after_initilize block to fix rails generator
error
Added Users controller to API