Fixes 3 issues found after deploying to stage:

  - undefined and NAN% was being displayed in text when student data didn't include correct or incorrect.
  - Items in radio display numbered incorrectly when student data missing options at the beginning.
  - Mouseover text included text from the correct and incorrect span.
Merge pull request #160 from Stanford-Online/dcadams/analytics_origin

Fixes 3 issues found after deploying to stage: