Make it possible to reconnect to a running match

Even if the game itself runs completely stable, it can happen that the wifi router goes haywire, the PC crashes or a player takes too long to find his laptop charging cable. In the course of a player drop in multiplayer, it should be possible for the player concerned to reconnect to the host from the lobby without all other players having to quit the current game. The transfer of the synchronised game data (in %) to the missing player should be visible to everyone as a small text output to increase transparency during the waiting time.