Utility enums: LanguageId, CountryId and CurrencyId

Practical to use for type safety instead of passing ISO-3166 (Etc)
strings around.
Code structure: Removed package 'enums'

Moved classes to parent package
Merge pull request #35 from iZettle/country-currrency-language-id

Utility enums: LanguageId, CountryId and CurrencyId