Expose current cell in a method

[danqing]

I'm subclassing DTPhotoViewController to add support for video, and I noticed that there's no method that exposes the currently visible collection view cell.

This is problematic for me because I need to access the cell in order to configure the AVPlayer instance I added to it. I can't do it in configureCell method because it's possible for a user to scroll a bit and then give up (thus returning to the previous cell), but other methods don't pass in the cell instance.

I suppose I can cast scrollView to UICollectionView and use that, but that's not future-proof. Can we have a way to access the current cell?

Thank you!

[tungvoduc]

Let's see if I can do anything about it this weekend. Also, you are welcome to open a PR :)