Make Mixologist idempotent, and make in not nest mixins
Stop using student_id in reference to scopes and ids in XBlock
Merge pull request #104 from cpennington/expunge-student-id

Stop using student_id in reference to scopes and ids in XBlock
Merge pull request #103 from cpennington/idempotent-mixologist

Make Mixologist idempotent, and make in not nest mixins