Product admits multiple entries of the same tax

[jorgeFons]

Its possible to add the same tax, multiple times, to a product. At the entity level this relation is modeled as a list, should'nt it be a set?

This leads to an incoherent state when issuing an invoice, GenericInvoiceEntryBuilderImpl.validateValues() @line314, with the tax amount being multiplied; Which is detected at GenericInvoiceBuilderImpl.validateValues() @line368.