As a user, I can choose to hide or not Test Sets when "adding them" to existing Test Executions or Test Plans

As a user, I can choose to hide or not Test Sets when "adding them" to existing Test Executions or Test Plans.

Whenever the user chooses to add the Tests of some existing Test Set, to a Test Execution or to a Test Plan, using the "Add Test Set" dialog, the user should be able to exclude or not Test Sets whose Tests are already included in those issues.

A new option, unchecked by default, should be added to the "Add Test Set" dialog available in the Test Execution and Test Plan issues.

"Hide Test Sets whose Tests are all already part of the current issue"

Note: in order to avoid misunderstandings, "Add Test Sets"  should be renamed to "Add Tests from Test Sets"  (in fact it's not the Test Sets which are added but the Tests that belong to those Test Sets).