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.
I guess this will have the effect of hiding previously earned points (from a time when they were enabled). Which... may be the desired behavior? (In which case, the `points_per_video` and `turn_off_points_for_videos` settings are somewhat orthogonal, and shouldn't be conflated as I suggested above...