[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
correction translation missing

Fixes #2463
edited admin/shipping_methods.js to be more explicit when manipulating checkbox inputs so that additional checkboxes are not affected

Fixes #2465
Don't change Property's presentation name if it's already set

Fixes #2455
Removes adjustments from incomplete orders

Every time a promotion is removed its adjustments should be removed from
incomplete orders

fixes #1046

fixes #2453