LPC-566 remove vat from parameters
fixing tests
keep vat as a parameter, but add deprecation warning when it's defined
removing tests concerned with invalid VAT strings
fixing signature in test after removing the vat parameter
adding a line in the changelog
moving change to the UNRELEASED list
Expanded deprecation warning for VAT parameter
Merge pull request #36 from laterpay/feature/LPC-566-remove-vat-parameter

LPC-566 Deprecate ItemDefinition vat parameter because of change in EU VAT laws