PACE 2020: at most three submissions per team

We decided that: 

1. we allow at most three submissions per team per track
2. in each track we rank teams (and not submissions) according to the best solver of a team. 
3. all the rules for submissions apply, in particular each submission should have its public repository and description.

Please note that multiple submissions are not supported by optil.io explicitly, so you need to create a separate user for each submission.