Add invoice condition template

Work in progress.
Based on https://github.com/OCA/sale-workflow/pull/50
Yes, it will be (just created the WIP PR here: https://github.com/OCA/account-invoice-reporting/pull/15).

But we will need to add such notice in https://github.com/OCA/sale-workflow/pull/50 since base_condition_template will no longer be there.