Implement TransitionViewControler sample

This pull request implements the Transitions sample with a few minor fixes:

* adjust the TOP_PLACEMENT to 70px so the image is not covered by the navigation bar
* use the now preferred shorthands for animation (e.g. UIView.transitionFromView:toView:...)

It'll also remove a pair of superfluous parentheses in the MainVC and correct the navigation bar tint to match the original.