[FIX] account_analytic_analysis: recurring invoices prepare and product_id_change

product_id_change set the description with the same behavior as sale orders
product_id_change set the price unit according to the pricelist
_prepare_invoice is split into two sub methods, _prepare_invoice_data and _prepare_invoice_line
_prepare_invoice actually prepare the invoice values instead of directly creating the invoice
[MERGE] Forward-port of latest saas-3 bugfixes, up to rev. 6958d47694df0a5397b07c40b061c41e43046941