Various issues with "Fresh tilled soil" demo

[aleclarson]

• [ ] The container doesn't change height based on number of items
• [ ] Items don't animate to their new positions (when shuffled or a preceding item is deleted)
• [ ] Double-click the "toggle" button while the items are visible, then double-click it again before the items have finished re-entering. Notice how the items that didn't start their "leave" phase won't animate their "enter" phase because they're already visible.
• [ ] Remove all items, then add a bunch of items really fast. Notice how the text says -Infinity and errors appear in the console. Then try removing one of the -Infinity items. Crash!