For importing and the deck creation wizard, we need to be able to generate
thousands of cards efficiently. So instead of requiring the creation of a fact
and rendering it, we cache the required fields and cloze references in the
model.
Also, emptyAns is dropped, as people can achieve the same behaviour by adding
the required answer fields as conditional to the question.
Todo: refactor genCards() to work in bulk, handle cloze edits intelligently
(prompt to delete invalid references, create new cards as necessary)
a4e8eb8b74