Improve Timeline UI

[chances]

Use TypeScript and my Component library along with the Object.observe() API, if available.

Also, use Duo!

Redesign add, delete, and clear buttons:

• Make their purpose more intuitive
• Redesign add button so that a time may be entered before the keyframe is created (Or perhaps auto-focused? Setup more configuration in Settings?)

Redesign playback bar:

• Different (pretty) buttons
• Add a seekbar
• Add a 'follow' toggle, to toggle whether or not the visible area should follow the scrubber

Hide overflow when bone label is wider than the list.

Adjust keyframe area width calculation so that if the visible area is the entire animation the scroll bar is not present.

Turn numerical inputs into spinners. (Time input should step by 0.1 second.)