Fixes a crash caused by moving a pinned layer to the top of the layer tree in
the Layers Docker. This seems to have been a side effect of changing the
return string of TimelineDocker::id() from "TimelineDocker" to
"AnimationTimelineDocker", so I've changed it back.

Because of this change, the Animation.kws workspace had to be updated
again so you may have to delete the old one in your krita configuration
folder.

Reversion introduced in e7bcb7e4 "Animation Timeline Docker: Settings Menu Widget."