Fix variant eager loading in Shipment `manifest`

See https://github.com/spree/spree/pull/3687
Allow users to dont split packages

Replay changes from https://github.com/spree/spree/pull/3618
Fix order_id assignment in OrderInventory

See https://github.com/spree/spree/pull/3712
Replace :confirm option by data: { confirm: "text" }

:confirm will be deprecated as of rails 4.1