removeTiles(tiles, fadeDuration) {
    if (_.isArray(tiles)) {
      for (let i = 0, il = tiles.length; i < il; i++) {
        const tileSprite = tiles[i];
        this.removeTile(tileSprite, fadeDuration);
      }
    } else {
      this.removeTile(tiles, fadeDuration);
    }
  }
Removes an array of tiles.
@param {Array} tiles - list of tiles to be removed
@param {Number} fadeDuration seconds over which to fade tiles