Fix potential tax calculation issues with charging of unreturned expedited exchanges

* Test that taxes are included
* Make sure to hit all state machine transition events

Conflicts:
	core/lib/tasks/exchanges.rake

Make sure not to ship again on an unreturned expedited exchange

Conflicts:
	core/lib/tasks/exchanges.rake

Fixes #5237
Allow Product.orders

One thing that our store admins need to do often is find the orders that have been made for a given product. This can be easily achieved by adding these `has_many through:` lines. This seems like a capability that other stores might find useful as well.

Fixes #5247