Add application category for OS X

Applications is often not subfoldered and View --> Arrange by Application Category helps but apps need to have this metadata otherwise they're sorted into "Other" at the bottom.  https://developer.apple.com/library/Mac/releasenotes/General/SubmittingToMacAppStore/#//apple_ref/doc/uid/TP40010572-CH16-SW8  (this applies to all Mac apps, not just those coming from App Store)