Verify Client VAT Number

Checks the client's VAT number against HMRC's Check a UK VAT Number service and records the outcome on their business details. When the practice's own VAT number is set on Practice Details the check is a verified one and HMRC's consultation number (proof of the check) is stored. A "not registered" answer is returned as registered=false, and clears any earlier verification. Editing the VAT number clears the verification automatically.