Redo the ExplorationTargetSet feature implementation
Current Status
The set feature of “ExplorationTargets” is implemented by a containment reference from ExplorationTargetExpressions to ExplorationTargets which is counter intuitive and was done due to backwards compatibility reasons.
Request
Move the reference to the ExplorationTarget class when the blocker is gone.
(from redmine: issue id 2963, created on 2017-05-18, closed on 2019-01-25)