* add more pricing detail to cart line items api:
- total line price, before any coupon/discount
- saving, aka discount amount (if any)
- boolean if saving > 0
* add new cart price info properties to schema
* tidy field naming – line subtotal=pre discounts, line total=discounted
* remove saving / discount fields from API – could be calculated on client
* return numbers (not string) for price fields
* rename API field "price" to product price for clarity
* fix schema type for total fields (now float)
* Total descriptions in schema
* Format all costs as strings to follow core rest api
* Add totals to cart schema
* Update tests
* tax_lines
e5bc742853