RandomImage constructor
      
      RandomImage(
    
    
- ImageType type
Implementation
RandomImage(this.type) {
  switch (type) {
    case ImageType.BOAT:
      _max = 18;
      break;
    case ImageType.FOREST:
      _max = 10;
      break;
    case ImageType.BULRUSH:
      _max = 12;
      break;
    case ImageType.RIVER:
      _max = 21;
      break;
    case ImageType.LANDING:
      _max = 8;
      break;
    case ImageType.CAMP:
      _max = 15;
      break;
    default:
      throw "Type ${this.type} was not recognized by RandomImage";
  }
  _currentRandom = _random.nextInt(_max!);
  _usedRandomNumbers = [_currentRandom];
}