UIButton+VerticalLabel.swift

// code from: http://stackoverflow.com/questions/2451223/uibutton-how-to-center-an-image-and-a-text-using-imageedgeinsets-and-titleedgei/24294816#24294816

extension UIButton {
  func centerLabelVerticallyWithPadding(spacing:CGFloat) {
    // update positioning of image and title
    let imageSize = self.imageView.frame.size
    self.titleEdgeInsets = UIEdgeInsets(top:0,
                                        left:-imageSize.width,
                                        bottom:-(imageSize.height + spacing),
                                        right:0)
    let titleSize = self.titleLabel.frame.size
    self.imageEdgeInsets = UIEdgeInsets(top:-(titleSize.height + spacing),
                                        left:0,
                                        bottom: 0,
                                        right:-titleSize.width)

    // reset contentInset, so intrinsicContentSize() is still accurate
    let trueContentSize = CGRectUnion(self.titleLabel.frame, self.imageView.frame).size
    let oldContentSize = self.intrinsicContentSize()
    let heightDelta = trueContentSize.height - oldContentSize.height
    let widthDelta = trueContentSize.width - oldContentSize.width
    self.contentEdgeInsets = UIEdgeInsets(top:heightDelta/2.0,
                                          left:widthDelta/2.0,
                                          bottom:heightDelta/2.0,
                                          right:widthDelta/2.0)
  }
}