answer statistics (logic)

Implement logic for answer statistics

This is a child of #10 (closed)

added ~1050 ToDo labels

assigned to @hdrs71

added WIP label

removed ToDo label

created branch 113-answer-statistics-logic

mentioned in merge request !85 (closed)

added 2h of time spent at 2018-03-14

changed time estimate to 2h

added 2h of time spent at 2018-03-15

mentioned in merge request !93 (merged)

closed via commit 774f0851

closed via merge request !93 (merged)

mentioned in commit 774f0851