Refactor and fix in `-buy_JSONForValue:` as well as other refactoring. Move a comment to where it is most applicable.

- switch from channelID to appID
- adjust API endpoints for products and collections
- adjust mocked responses

This adds a attributes to checkout. These objects are returned as an array of dictionaries, but expected as dictionaries when posting the checkout, so we're required to serialize the objects correctly. API now also returns the `note` on a checkout, so I have added a test for that.

"/anywhere/checkouts" is now "/api/checkouts". This transition has been made using NSURLComponents. Tests have been updated to better match testing of the scheme, host, path and query items from which a NSURLComponents URL is created.

Fix an issue where partialAddresses flag was set to false, which would invalidat the already set (through a updateCheckout: call) shippingRate on a checkout during completeCheckout:

Refactor partial address handling to prevent a partial address to be applied on a completed checkout

fixes for integration tests

fix partialAddress unit test

Allow for partial address flag to be set to false on update

Prevent partial address from being sent post Apple Pay authentication

This adds a attributes to checkout. These objects are returned as an array of dictionaries, but expected as dictionaries when posting the checkout, so we're required to serialize the objects correctly. API now also returns the `note` on a checkout, so I have added a test for that.