SelectionHandler
SelectedItems
Until now it was up to each implementation to connect `BlueprintContainer` to its `SelectionHandler`, which didn't make much sense at all.
Removed some words but also don't mention "smaller" because it's... musically incorrect and also functionally incorrect – entering 1/[8] will result in 1/16 also being populated for instance.
TimeSignatures
TimelineSelectionHandler
var