Show the submission used for a scrimmage #891

It would be cool, as per competitor request, if we could see the submission used to compete in a match. This should be doable by listing the description of the submission on a given scrimmage. We list scrimmages in scrimhistorytable.tsx, and it should be possible to get the participants' (the user's team) submission directly from the match! So should be a fantastic slam dunk. Let me know if there is any confusion.