Create subtitle! (successfully)

[rayastar]

1. add subtitle label to BTNavigationDropdownMenu.swift: fileprivate var subTitle: UILabel!

2. Create label:

   let width  = titleSize.width + (self.configuration.arrowPadding + self.configuration.arrowImage.size.width)*2
   let height = self.navigationController!.navigationBar.frame.height
   let frameForSubTitle = CGRect(x: 0, y: 14, width: width, height: height)
   
   self.subTitle = UILabel(frame: frameForSubTitle)
   self.subTitle.text = items[0] as! String
   self.subTitle.textColor = self.menuTitleColor
   self.subTitle.font = UIFont(name: "Avenir-Heavy", size: 10)
   self.subTitle.textAlignment = .center
   self.menuButton.addSubview(self.subTitle)

3. Edit : func setMenuTitle(_ title: String) { self.subTitle.text = title }

Result: