Add /config/money endpoint so that API clients know Spree's money settings
[api] Rename line item display_single_amount -> single_display_amount (to match Core's API), display_total_amount -> display_amount and add total
[api] Add token to order data responses
[api] Allow orders API to accept an order token to verify authorization of request
Remove set_expiry before_filter as it was causing too-aggressive caching of pages
[api] rename token parameter for API to order_token to stop it clashing from API key token param
[api] Ensure that passing through line_items params hash with an ID works
[api] Authenticate line item creation using order_token
[api] Correct attributes check in line items controller spec
[api] Updating an order's line items to set a quantity will no longer add quantity to existing total, but rather set total to quantity passed in.
[api] LineItems#create will now increase quantity of existing line items, rather than creating duplicates
Downcase s3_protocol configuration option to prevent bugs like https://gist.github.com/radar/5793814

As seen in: https://groups.google.com/group/spree-user/browse_thread/thread/152ceac667a80147
[backend] Correct translation key in locale_spec
Ensure quantity is coerced to integer in OrderContents#add_to_line_item

It *might* come from a controller parameter, which is a string. The API's LineItemsController#create action does this, for instance.
[api] Cache-Control headers are no longer set per-request
[api] remove test for adding line items with an update call

To add a line item, you should make a request to POST /api/orders/:number/line_items
if a product only has images for its variants, display the first variant image for the product instead of none

Fixes #2992
[backend] No need to set state to complete for factory in payments_spec
Don't blindly set bill_address_id and ship_address_id to nil in order factory
Fixed notification when Gemfile.lock not exists

Related to #3205