Pricing

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | yes
| Deprecations? | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | *to be written*

Expanding on what @umpirsky started, this is my promised take on pricing bundle with quite flexible price calculators. It also includes duplication removal for the registries. They live in ResourceBundle for now, but will be moved to standalone component in future. More will follow. (shipping bundle registry)

I think we need even more than that... like price rules with logical conditions, but it is a good start and gives us great dose of flexibility.

* [x] Rethink the cart prices recalculation logic and implementation. (which events, move logic outside the listener)
* [x] Add the configuration form for volume based calculator.
* [x] Make the scenarios pass.
* [x] Fix the spec of form listener.