Make battles happen on their own thread.

[Alberdi]

This would give the game a more frenzy pace because you could have a lot of battles going on at the same time. Also, it would allow more than two players without being forced to be paused to watch battles where you are not participating.

Last time, I tried to create a new window for each battle, but the library kept crashing. Maybe we could simulate it or find a workaround.