[tryton] Change decimal precision

[Αργύρης Ξηρός]

Hi,

Is it possible to change decimal precision of the: 

   - product (product_price) and 
   - invoice_lines (unit_price) 
   
from 4 to 7? So I can have more precise prices in the invoices?

Do I have to change it in the modules or i have to make one on my own?