Meaningful constants

[DragonBe]

When we first started out creating this service, we only looked at validation of VAT ID's for EU countries and named our constants in such a way that we weren't ready for other validation types.

Now with issue #82 a new type of validation was presented for companies outside of EU that require a VAT ID to perform business within the EU. We have implemented this validation already in PR #85 but the naming convention of the constants VIES_EU_COUNTRY_TOTAL and VIES_EU_COUNTRY_LIST no longer represent their true values.

These constants require to be changed into a more meaningful label that reflects this new situation.

[Seldaek]

Moreover, the listEuropeanCountries function should not return 'EU' as a european country code IMO, regardless of what the constant is called.

[krzaczek]

@Seldaek yes the listEuropeanCountries should not return EU.

We could do this two ways

1. We could leave EU in the list of VIES_EU_COUNTRY_LIST and just update the listEuropeanCountries to not return EU as a "country" by simply filtering the return array.
   or
2. We could remove EU from VIES_EU_COUNTRY_LIST and write a new method to validate requestor prefix (that should return true for all 28 countries and EU

I think we should go with option 1) since probably (don't know why it's not working this way now) VIES will allow to validate EU MOSS VAT numbers in the near future, and we will just need to rewrite the ValidateEU class to make it work.

[Seldaek]

@krzaczek implemented 1) in #87 - it doesn't fix the const naming issue but at least the public API is now fixed which I hope makes it ready to release.

[krzaczek]

@Seldaek Could You fix the PHPCS errors so we could merge it and release it #87 (comment)

[DragonBe]

Closing this issue as PR #87 is now integrated in master code and will be released soon.