Host quitting rated games

[elexis]

Often players on the lobby quit the game in order to avoid getting a negative rating.

A simple and strict approach would be to reduce the rating if the server disappears, even if it was a power blackout or a crash.

A less strict approach would be to detect the shutdown. Both clicking on the exit button and closing the game with Alt+F4 (sending the exit signal) can be catched in the destructor of the CNetServerWorker() for example (maybe we can find a nicer place). The host quitting the server could send a packet to the lobby that he just quit a rated game. This means abuse can also be tracked, allowing more accounts to be banned.

[elexis]

Notice there might be a good reason to kill a rated game. For example the game might be unplayable due to network lag or the game taking too long. The players could accept a draw (vote) which wouldn't change the rating (#2512). Otherwise the lagger / absent party would be declared to be defeated.

Also if we only punish the host for quitting a rated game, then the clients can still quit to avoid a rating (and we shouldn't trust the host if he says that that guy left).

Instead we could limit rated games to games hosted by Wfg on a dedicated server using #3556. The server would be able to verify who goes absent or lagged too much for too long and inform the lobby bot to adapt the rating.