Convert tournament from useRef to useState

In the Tournament component, convert from a ref:

    const tournament_ref = useRef<TournamentInterface>(...);

to a state:

    const tournament = useState<TournamentInterface>(...);

This enabled the following additional changes:

- Remove `refresh()`.
- Removing redundant state, switching to `useMemo` for `sorted_players` and
  `raw_rounds` and local variables for others.
- Reset non-tournament state when `tournament_id` changes.

Depends on online-go#2575 (builds on top of it).