See https://github.com/ankitects/anki/pull/900#issuecomment-758284016
- Leave tag names alone and add the collapsed and config columns to the tags table.
- Update The DB check code to preserve the collapse state of used tags.
- Add a simple test for clearing tags and their children
- .update() should update a single deck and preserve usn by default,
as that's what existing code expects
- decks are automatically renamed when they conflict with an existing
name
- notes with wrong field count are now recovered instead of
being deleted
- notes with missing note types are now recovered
- notes with missing cards are now recovered
- recover_missing_deck() still needs implementing
- checks required
