Refactor folders

[octaviusz]

I'm just farming Additions and Deletions

[mr-cheffy]

How's it going? Whats left?

[octaviusz]

• Refactor element position restoration. Current prevTab.after(tab) is too brittle and depends on order; throws an exception if prevTab is still in groupActiveTabsContainer.
• Investigate why elements from other spaces are visible on startup. (I might need to set the overflow).
• Implement animations for appearing tabs in LiveFolders.
• Add collapse/expand animations for folder movement (animateGroupMove).

• Tests, tests, and more tests.
• Anything else I’ve inevitably forgotten.