slapos_subscription_request: WIP: stop using discount resource, and reduce the quantity of the consumed software product / service

See merge request nexedi/slapos.core!629

  No need to always set those properties, while no accounting is setup.

  Let the project introduce it if they rely on those payment modes.

   Use subscription_list to calculate Balance amount for the ledger, currency, section from the list. It keeps consistency with the Entity_createDepositPaymentTransaction implementation.

   For now we rely on Base_createExternalPaymentTransactionFromOutstandingAmountAndRedirect for pay subscriptions for customer organisation because it requires update security and review the procedure and how UI will handle it.

  So we invoke directly Entity_createDepositPaymentTransaction with the organisation's subscriptions.

   Use acquisition properly.

   Same as Sale Invoice Transaction to generate payments.