Order And Fulfillment Instructions

Customer instructions are now called instructions everywhere. The order detail reads and writes through the new field, and fulfillment instructions behave the same way gift messages now do — a fulfillment's instructions override the order's if set, otherwise the order's instructions apply. Packing notes sent to ShipHero and Packiyo use whichever value resolves.

The older note name is kept as a compatibility alias for anyone reading or writing through it, so nothing breaks — but new integrations should reach for instructions.