Heading into WWDC 2013, Apple had a lot to prove. The company was still licking its wounds from the botched launch of Apple Maps in iOS 6, and complaints had been growing around iOS’s increasingly stale design. Though the iPhone was by then a proven hit, iOS was starting to look outdated. Remember the notepad-like Notes app? The weird linen background behind Notification Center? The felt-ish green background of the Game Center app? When compared to things like Microsoft’s very flat and,…