Byoyomi periods for correspondence games.

[AlexGTrick]

We started trying to organize a Chu Shogi correspondence tournament. The intent is to set the time control not too demanding (1 day per move) and not too long which will make the tournament last extremely long (5 days per move). The obvious choice is something between 2-3 days per move. But it is not the best possible variant for the tournament.

1 day per move is sufficient if we have periods of byoyomi extensions, about 15-20, one day each.

Unfortunately, right now on Lishogi the concept of "byoyomi periods" is unavailable for correspondence games. "Days per turn" effectively works as byoyomi, so I would also suggest renaming it to "byoyomi" while introducing "byoyomi periods" for correspondence.

That's also helpful to make it possible to set the duration of byoyomi separately to byoyomi periods as mentioned in issue #718 That will allow us to set byoyomi 1 day and 10 periods of 2 days each, which will work fine in tournaments too.

The possibility of setting different initial times for players mentioned in #740 will help very much too. It will make it possible to effectively introduce "vacations" during the tournaments (duration of 7-10 days, for example) that work like adjournments. Players want to continue the game with their actual byoyomi period available at the moment of the adjournment.