Replicating some UIActionSheet delegate methods (and copied these behaviours to blocks as well). Also added buttonTitleAtIndex:

I've added a number of delegate methods from UIActionSheet: `willPresentActionSheet:`, `didPresentActionSheet:`, `didDismissWithButtonIndex:` and `willDismissWithButtonIndex:` and replicated these types of callbacks in the block-based callbacks. I also added it as a method on RDActionSheet `buttonTitleAtIndex:` just like UIActionSheet that returns the title for the button at the specific index. I updated the block-based callbacks to return the title action well so the developer doesn't have to create a weak reference to actionSheet in order to check the buttonTitle on a buttonIndex.