Vathandler

Here is the vatHandler. Seems to be working. 
Some things to note
* I needed to change converter because we were dealing with dataText[0] for the isVatIncluded thing, but that value is not the first but the second. 
* Fixed some tests too after the change of array $price to PriceValue $price

Edit: Now i've added exceptions:
 * Created two new Exceptions class
 * One is general so every Gateway can't use for cases when VatRate is not found
 * Other is "Legacy" specific, for the case when vat automatic is used

Actually, I think I intended to cast it to `(int)` (should work).