Account Calculation; better validation of Account Type Promotion

The finPOWER Connect Business Layer "Account Calculation" validated some aspects of the selected Account Type Promotion, e.g. that it wasn't closed and that the Dealer was allowed. However, it did not validate the Branch and Broker filters.

Additional checks have been added whenever the Account is calculated.

WARNING: This is flagged as a breaking change as, although the User Interface only permitted valid selections of promotions, the Business Layer would allow invalid promotions where the Branch and/ or Broker disallowed the Promotion.

Note, the Account.Calculation.LoadAccountType function's DealerExternalParty parameter is now noted as obsolete as it has no effect.