New rows: cohort % and event %

[dirediredock]

Per model, compute cohort % and event % as data to visually encode.

Feedback: "Can you add two additional rows to the table with the risk distribution? Adding a row for cohort percentage and event percentage would help our group understand how many patients and events are captured in each group. I find that with many of these risk scores, although the rate of events is low in the lower scores, more patients have these scores, so there are a significant number of events that occur in these smaller risk score groups."