Added MXLMediaView spec

MXLMediaView was created for our own apps at MobileX Labs. I wanted to implement the 'display style' that a lot of other apps are using nowadays when the background blurs and shrinks (Facebook, TweetBot, etc). But I wanted my own little twist. I decided to take advantage of the nifty UIKit Dynamics library added in iOS 7 to have the media drop and bounce onto the screen.