Support resetting the animation for reuse

[pinglamb]

I am using RazzleDazzle to animate items in a collection view. The problem I came across is that the cell views are reused and animations configured before need to be cleared. I added #removeAllKeyframes so that I can reuse the same animation object attached to the cell.

The code while preparing cell for collection view:

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! Cell
        var animation: ScaleAnimation // ScaleAnimation as example
        if cell.animation == nil {
            animation = ScaleAnimation(view: cell)
            animator.addAnimation(animation)
            cell.animation = animation
        } else {
            animation = cell.animation!
        }

        animation.removeAllKeyframes()
        // Set up the animation here

        return cell
}