Add blank? method to assessment items for checking for completed answers.
View for "Run Details" list for runs for a class assignment   [#84708072]

https://www.pivotaltracker.com/story/show/84708072
Only include non-blank answers in Run#num_answers
Controller and routes for "Run Details" list for runs for a class assignment   [#84708072]

https://www.pivotaltracker.com/story/show/84708072