"State" is not passed to promotion action `onActivate` function

[michaelbromley]

Is your feature request related to a problem? Please describe.
Requirement: a promotion like "for every N of Product A, add free gift B"

Currently this is not possible because the value of N (which would be calculated by the PromotionCondition and passed as state to the PromotionAction) is not available in the side-effect API methods onActivate and onDeactivate. Thus there is no way to know how many free gifts to add.

Describe the solution you'd like
Add a state arg to those functions, passing in the data object from the dependent promo condition(s).

Describe alternatives you've considered
Re-implement the logic in the action to calculate the number to add, but this is bad for efficiency and maintenance.

[dlhck]

Note: This issue needs to be expanded to generally think about the current implementation of promotions. Therefore more research needed.