add an override parameter to the decorator module
add last_in_session and rolling_success to the decorator
be able to compute, load and store the difficulty
be able to compute, load and store the prior skill

also be to compute number of answers per user
compute statistics over time
work with rolling succcess
create requirements.txt
compute portion of users per session
work with prior skill and success rate in sessions
a bunch of new graphs and improvements
improve A/B testing statistics
improve overview statistics