Presents and dismiss a controller with an expanding bubble effect.

let transition = BubbleTransition()

public override func prepare(for segue: UIStoryboardSegue, sender: Any?) {
  let controller = segue.destination
  controller.transitioningDelegate = self
  controller.modalPresentationStyle = .custom
}

// MARK: UIViewControllerTransitioningDelegate

public func animationController(forPresented presented: UIViewController, presenting: UIViewController, source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
  transition.transitionMode = .present
  transition.startingPoint = someButton.center
  transition.bubbleColor = someButton.backgroundColor!
  return transition
}

public func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
  transition.transitionMode = .dismiss
  transition.startingPoint = someButton.center
  transition.bubbleColor = someButton.backgroundColor!
  return transition
}

var startingPoint = CGPointZero

var duration = 0.5

var transitionMode: BubbleTranisionMode = .present

var bubbleColor: UIColor = .white