Remove unneeded 'model' attribute from HistoryView and delete useless spaces
Use a more pythonic way of testing an empty list
Get rid of the dispatch method in HistoryView
Add test for detailed_challenge_stats
Use 2 different views for challenge stats and hook them on different urls
Cover the case when a staff user wants to see the stats
Create get_stats method in ChallengeUser model
Rewrite views