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.
Not sure whether this is best (might be better to do it as a block helper, with Handlebars variables instead of `sprintf` syntax), but works for now:
https://github.com/rtibbles/ka-lite/pull/7/files