Incorrect accuracy chart / wrong participant count in the task

[MIDAV0]

Accuracy chart logs incorrect data, as well as final accuracy always displayed as 0.

[MIDAV0]

The issue with number of participants
Training workflow:

1. User joins the task in the client
2. Contract records that user joined the round
   a) If round is in progress then user will join next round
   b) If training haven't started user will join current round
3. Contract records participants from scratch every round (start at 0 and users join automatically if they were in previous round)

Issue right now is the case when user joined the round and during the round they log-out of the client (just close it or encounter some issue). Contract does not record the fact that user dropped out of the round. This issue also may affect the rest of the contract logic.