Implement various game modes

[christopherbot]

allow player to select different game modes:

• snake pong mode (split screen pong with a snake as your paddle)
• snake breaker mode (same as above except hitting the ball causes that part of the snake to break, and the tail falling off)
• dual snake mode (two snake games in the same map)

allow player to select number of players

• 1 player (solo, vs. computer)
• 2 player (local, online)

[christopherbot]

Look into Colyseus as a multiplayer game server