tictactoe: Adapt to new server event type: game-state

Previously, when a client joined a game in progress the server would
send all previous moves as "move" events (just the same as if a player
were making those moves live).

The server was recently changed to instead a single "game-state" event
in this case, (which also does contain the entire move history). So
when we receive that, we reset the game state, then replay the moves
from that history.