Ability to toggle visibility of timeline object tracks from the outline 🙈

[juniorxsound]

Context

Since the outline list is a full height scrolling list, it's pretty easy to navigate it even as it grows (albeit IMO namespace collapsing would still be helpful #356). However when the timeline list grows it becomes hard to keep track of the entire list (even when collapsing objects). It'd be nice to add an outline show/hide icon that toggles between showing the object track in the timeline and hiding it. Was imagining it'd still play it's animations even when hidden but would give you the ability to focus only on the animations you are currently working on.

[donmccurdy]

A few alternatives that might similarly help with managing large scenes:

• Searchbar on the Outline Panel
• Searchbar on the Sequence Editor
• "Focus Mode" on the Sequence Editor, in which only the selected Sheet Object's keyframes are shown

I'm imagining the searchbar(s) would just temporarily hide items that don't match the query, similar to the searchbar on https://threejs.org/docs/. Would be happy to file separate issues for these ideas if that's any help, but they seemed closely related here.