Fix backend order split shipments action

When moving an item to a existing shipment from the same stock location
it would make two requests to remove items from the same shipment.
Instead it needs to remove from one shipment and then add the same
quantity to another shipment

[Fixes #3161] [Fixes #3162]
Fix build specs and split shipment edit button [Fixes #3167]

They were mostly failing due to a js error and shiping labels
Ensure correct classes on stateSelect, stateInput elements in address
spec

Fixes #3165
[api] Remove caching of products (index+show) + taxonomies (index) actions
Return Cache-Control headers for all API requests