Price list with tax included
Discussion: https://groups.google.com/d/msg/tryton-dev/egoUf_eZUoo/X8mR_QxIfNkJ
The idea is to allow to define price list with tax included and to compute back the unit price without taxes to put on the sale.
It still need to decide if the tax rounding should be enforced.
If the price tax included should be displayed on the lines/report.