Spree::Zone#country_list fix

Just fixing wrong default value of case expression - should return an Array instance, ie. `[]` instead of `nil`.

Fixes #4827
Add missing translation.
Add state_text to StockLocation

I'm working on a revision to `Spree::TaxCloud`, and we use the `StockLocation` addresses pretty heavily. It'd be a huge help to have the `state_text` method that exists in the [`Spree::Address` model](https://github.com/spree/spree/blob/master/core/app/models/spree/address.rb#L39).

Fixes #4872
Removing unnecessary controllers and views from the admin
Fixes #5280