Burying: UI changes, catch up to new commits, and some fixes

This is built on top of the branch in my other pull request. I suspect GitHub can figure it out once you merge the other one. I thought I'd put it up for review while I can since we're running short on time.

Anyway, these changes add the new UI elements for the new burying behaviour, namely the new options in the options groups that replace some older sibling spacing ones, and an unbury button in the "congrats screen".

I also added the new commits from today (yesterday) and fixed a couple broken queries after testing it. I also removed the "return to study screen" button from the congrats screen since we need more space after adding the new button. It achieves the same thing as the back button, so I figured it didn't need to exist (we've discussed this before on the forums).