Promises for pricing calculator

Signed-off-by: Christopher Rogers <chrissrogers@gmail.com>
Adapts pricing calculator to use PricingPromises

and moves PricingPromise into its own module

Signed-off-by: Christopher Rogers <chrissrogers@gmail.com>
Fixes PricingPromise done reprice calling

Signed-off-by: Christopher Rogers <chrissrogers@gmail.com>
Fixes PricingPromise to pass along its bound pricing instance

Adds tax processing to dom binding change promise-based control flow

Signed-off-by: Christopher Rogers <chrissrogers@gmail.com>
Fixes tax options object mutation

Signed-off-by: Christopher Rogers <chrissrogers@gmail.com>
Adds property method wrappers to PricingPromise instances, and adapts pricing dom binding to the new methods

Signed-off-by: Christopher Rogers <chrissrogers@gmail.com>
Adds full suite of Pricing methods to PricingPromise wrapper

Signed-off-by: Christopher Rogers <chrissrogers@gmail.com>
Adds fallback callback support to Pricing

Signed-off-by: Christopher Rogers <chrissrogers@gmail.com>
Fixes blank coupon adding and item removal

Signed-off-by: Christopher Rogers <chrissrogers@gmail.com>
Fixes PricingPromise to properly chain promises not given in a single call chain

Signed-off-by: Christopher Rogers <chrissrogers@gmail.com>