Add custom transitions to dialogs

[Sadeesha-Sath]

Love this package. It's such a life-saver. However, I have written an app with a custom transition animation for all the dialogs it has. But since this rate dialog cannot be animated, it looks out of place.

It would be so much better if we can add custom transition support to this package.

I think it will make this package a whole lot powerful.

If it already has a way of animating and I'm missing it, please correct me.

Thanks

@Skyost