Add validation for European Union EORI

[pokoli]

This is an initial version of the module as it only validates the standard format of the identifier.
As the identifier is composed by a company prefix, there should be a local validation for each country but I'm not sure of the format of all countries (I can investigate if there is interest of implemeting it). I have two examples:

• For Spain: The EORI validation is the vat validation.
• For UK: The EORI is the VAT plus three numbers (normally 000)

There is also a webservice in the EU to validate if the EORI is valid which may be implemented in the module (as we do for VIES).

I dediced to keep the changes small and get some feedback in which features should be interesting for the library.