Re-group add to cart specs
Fill in some missing / incorrect test cases for add to cart
With order cycle distribution, show error message when adding a product to cart with no distribution chosen
Rename DistributorChangeValidator to DistributionChangeValidator in preparation for expansion to include order cycles
Cherry-pick c3b2f52: Cache DistributorChangeValidator#all_available_distributors, move Enterprise#available_variants into SQLland - massive render speed improvement

Conflicts:

	app/models/enterprise.rb
	lib/open_food_web/distribution_change_validator.rb
Fix minor test fail
Add OrderCycle distributing_product scope
DistributionChangeValidator finds available order cycles for a product
Refactor DistributionChangeValidator#available_distributors specs
Add DistributionChangeValidator#available_order_cycles, analagous to available_distributors
Add OrderCycle#distributed_variants
Add first product to cart with order cycle choice