Surface more data for instructors (without downloading anything)

[lenglund]

Instructors/instructional teams see PI as a black box, and it's unclear how to use this tool to help with teaching and learning unless data is clearly and efficiently made available. Basic data should include: how many students completed part and/or all of the exercise, how many students changed and/or revised their answer (could be same as student histograms), and how many answers were tagged by students (either inappropriate re: #61 or otherwise marked #135, if implemented). More advanced data could show: how many students were potentially swayed by each answer (when this answer appeared, # changed their answer in some way) and time spent on each step. This can all be added to the staff debugging.