* Adjust type to remove cards from the queues, so we don't have to rebuild
priorities to restore them:
Type -= 3 when suspending
Type += 3 when burying
Type += 6 when cramming / reviewing early
We still need to adjust priorities for backwards compatibility, but this can
be removed in the future.
* Factor out scheduler-specific code in answerCard(), so the different
schedulers are now fully modular
* Differentiate between a card's current queue and its type
* Make sure dueCutoff cuts off at the chosen offset instead of midnight