Add Copy,Cut and Paste of build targets and sets
- Add Json serialization to and from TargetModel QModelIndexes
- Add Copy, Cut and Paste using the json serialization
- Use the serialization for Project targets
- Change the SaveProjectTargets to be triggered from the model (Copy/Paste would otherwise not be handled properly)
- Group saves to one if there are multiple project changes
TODO:
Use the serialization also for session targets and make Command and TargetSet private in TargetModel to not leak implementation details.