automatically add Customer/Supplier to VAT ID check

[Mutantpenguin]

On creation/modification of a Customer/Supplier, a VAT ID check should be automatically created if:

• a VAT ID was entered
• customer_primary_address/supplier_primary_address is filled
• this address is located in Europe
• only if no check already exists for this Customer/Supplier and Address

We would do this for our own internal app anyway, so I am more than willing to create a PR if there is interest in such a functionality.

This would include a rough validation of the VAT ID already in the Customer/Supplier. This is only a check if it's technically a correct VAT ID, and not if it really exists.