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.

   Merge Deposit and Invoice payments under the same (or nearly similar) implementation.

  Reimplement Entity_addDeposity by creating deposit from a list of subscription

  Ensure will transfer deposit to the proper organisation/person, ledger
  and currency.

  Payment Transaction must preserve website context otherwise it will
  fail over redirections later on.

   It must lead to "Contact us" page. Allow us use accounting for other configurations, so it
   allow the user generate a payment and contact us to make the wire transfer or pay from
   some non-automated system.

   Since payzen/wechat depends on specific currency, so keep default implementation generic, so it allows the user get a contact us message, so it permits the system use wire transfer or non-automatic payments, to proceed with payment.