Add a defaultModalPresentationStyle API for transitions with presentation.
Summary: This allows transitions with presentation to choose the default modal presentation style for a view controller. This is necessary because the transition may choose not to use a presentation controller even though it conforms to the TransitionWithPresentation protocol (e.g. a modal transition that covers the whole screen may not need a presentation controller).
Tags: Material Motion
Differential Revision: http://codereview.cc/D3230