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.
This change can be simpler - just remove `MaintainCustomerMasters` from the list of privileges in the Sales menu item for [Update Credit Status By Customer](https://github.com/xtuple/qt-client/blob/4_7_x/guiclient/menuSales.cpp#L316).

However, `MaintainCustomerMasters` is part of the list in the Sales menu because anyone with access to the Customer master window or Workbench automatically has the ability to change the credit status, regardless of the `UpdateCustomerCreditStatus` privilege. Changing _that_ would break with long-standing precedent (we do not control individual screen and database fields in the Qt client) which means that the code change to `customer.cpp`
- would be much larger than it sounds
- risks making people more unhappy than issue #23832 itself

Does anybody have an opinion on what to do here? Bug #23832 was reported by QA in 2014 but the current menu item privileges go back at least as far as 2009.