[FIX] website_sale: product website description must be translatable
[FIX] account_budget: theoretical amount: ignore future and use datetime
[ADD] account_budget: theoretical amount: tests
[FIX] account_payment: fixed the view of payment order to display the amount of transactions
[IMP] account_payment: remove dead voucher code and extension hook

Since bank statement do not use vouchers anymore in 8.0,
it's not necessary to create the voucher anymore.

Additionally, I add an extension point to let modules adapt
the statement line.
[IMP] doc: try to clarify what $as is in qweb doc
[FIX] Avoid access error on XML id in browse when choosing picking type for manual purchase order.  As they are ordered by sequence, just take the first you can find.