Serialize the setting of asset on transition

And simplify the way we write action in the file
application: Add 'wait' action between actions

+ stop everything when quitting.
clipproperties: Commit the timeline when removing an efect

+ No need to flush the pipeline if we already commited (and now
that the commit actually had the same effect)
effect: Serialize effect related actions
undo:timeline: Do not track transitions addition

It is all automatic so we should not let user do or undo their addition