Feature Request: Dismiss Callbacks

[otymartin]

@HarshilShah

Would it be possible to add callbacks for events willDismiss and didDismiss to run code on or during those events. For Instance, I use the Hero transition library for certain transitions and it conflicts with DeckTransition. I would like to be able to turn it off so it's behavior doesn't interrupt DeckTransition's dismiss animation.

[HarshilShah]

This is a good idea, I’m adding it to the checklist for an upcoming release. See #109 for more about that.