Implemented legacy VatHandler

Introduces a VatService, that uses a Vat handler, with a legacy implementation.
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
Adds an `ezprice_value` twig function that transforms a `Price\Value` to a `PriceWithVatData`, that aggregates the original price data with `priceIncludingVat` and `priceExcludingVat` properties.