Network Multiplayer

[ClaCodes]

• Make use of renet for network multiplayer.
• Implement server async using tokio. For now every player has their personal game/lobby -> more work needed for configuring server, then lobby for joining and creating games, then all players press ready, then a round is played, after game ask for rematch ... . Also the "game over"-handling is not yet correct. It just hangs forever.
• Adjusted ui_cli to become a renet-client -> works.
• WIP on adjusting the bevy client to become a renet-client using the existing plugin bevy_renet -> should not be to difficult, since it communicates with server now instead of with separate game-thread. But I could not get it to connect to the server yet.
• I reused a bit of code in bevy for the server. So I moved it to core for now.
• For now using json as message encoding. Since it is a turn based game probably ok, but I wanted to experiment with other.
• reformat, clippy, warnings, ... just an rfc
• server may be leaking tasks on client disconnect