Allow teachers to perform a forced sync via web interface button.
Make AttemptLog.context_type optional to avoid sync errors on old data.
Merge branch 'nalanda-rct2' of github.com:learningequality/ka-lite into nalanda-rct2
only show student scores if total number of answered questions is greater than 0
Adds default value for total_correct on quiz_logs to prevent error
where first correct answer was discounted.
Added regression test for quiz not registering correct answer on first question.
Merge pull request #2328 from rtibbles/quiz_log_fixes

Fix to prevent first correct answer on a quiz not being counted in the total_correct field
Merge pull request #2335 from learningequality/nalanda-rct2

Nalanda rct2 into RCT3