Zip Code Zones should consider countries

[fthobe]

Zip codes are not unique, many countries can share the same numbering format (108 countries use 5 digit zip codes creating lots of duplicates).

[fthobe]

@DanielePalombo @tvdeyen was this already made at Nebulab or Blish?

[tvdeyen]

@fthobe one of our clients has a Zipcode model that belongs to a Spree::State and through that to a Spree::Country if this answers your question?

[fthobe]

@tvdeyen can you share the relevant parts and we bring that over to adjust the zone model?

[fthobe]

@tvdeyen can you share the zip code state model?