Provide command to modify game-join timeout

[calebtote]

While there's a command for the player action timeout, there doesn't appear to be a command to modify the countdown for new players to join a new game. The default is 30 seconds

 // Returns an {Observable} that will `onNext` for each player that joins and
  // `onCompleted` when time expires or the max number of players join.
  static pollPotentialPlayers(messages, channel, scheduler=rx.Scheduler.timeout, timeout=30, maxPlayers=10) {
    let formatMessage = t => `Who wants to play? Respond with 'yes' in this channel in the next ${t} seconds.`;
    let timeExpired = PlayerInteraction.postMessageWithTimeout(channel, formatMessage, scheduler, timeout);