Persist the selected clips when undo/redo and the clips are removed/re-added
If you:
- add one clip to the timeline, then
- add another clip,
- select them
- undo, notice a clip is removed from the timeline
- redo, notice the clip is added back but it's not selected when it should be.
If the Layer instances report to the project.ges_timeline.ui.selection
the clips added and removed to themselves we could put the removed ones in some automatically_select_pool
field, and when they are added we can automatically select them.
Depends on #2409 (closed)