#to_package Use symbols for state. Fixes #3326

From Original Issue: 

Calling `to_package` on a Shipment (as done in `refresh_rates`) creates a Package with invalid inventary_unit's states - i.e. it uses strings for the state of the inventary unit instead of symbols (expected).

To reproduce:
```ruby
package = my_shipment.to_package
package.backordered # will always return an apty array []
package.on_hand # same thing, empty array
```