Nalanda RCT3 Cleanup

Summary of changes:
* Display total correct when quiz completed.
* Switch StoreItem over to non-Django model.
* Award points for questions answered correctly on quizzes (based on server side basepoints).
* Increases seed across all items in a test so that no two items in a test have the same seed.
If they're not always the same, there is a problem. In fact, this.get("attempts") is encoded by the length of the response_log, so we could collapse the two.