Add "average score" to summary statistics

Currently, the summary statistics include the total number of questions and responses, the average number of curiosity points, and the total number of curiosity points. However, at least in some cases, students scores for each question/response depends on the corresponding curiosity scores. As a result, for students to determine their average score, they have to go through each interval and do the calculation manually. I would make much more sense to add one additional field to the summary statistics and calculate this.