Case list/detail page redesign (revert revert)

Original PR is here: #4553 (with discussion).
This reverts dimagi/commcare-hq#4574 (which reverted #4553).
How many apps + app builds are there? If it's a lot we should probably bulk-save these instead of saving them one-by-one.

Also I think this is correct, but be aware you're migrating app builds as well as app. I think it's the correct behavior because if you revert to an old build, you want the new-style app.