Privilege check added to update function and message

Based on bug report, menuSales.cpp was reviewed and detected that menu privilege check is OR linked with CustomerMasterMaintain so CustomerMasterMaintain activates the menu option. The behavior requested by the bug will make the utility to work only having the update credit status privilege. As bug is confirmed I have programmed the privilege and a error message if the user don't have it.
I'd be content if UpdateCustomerCreditStatus meant that if you had the priv, you could update the credit status, and if you didn't have the priv, you couldn't update the credit status. If this PR aligns the app to that understanding, and if any simpler solution might make people unhappy, then I'd say this PR is a good fix.