Locked reading/audio play from stock

[Frost015]

Adding the option to mantain a book opened (using volume keys to forward/back page) when locking the screen would be a nice addition. It was present in stock although it didn't work with every e-book app (Moon Reader Pro sadly didn't work with it). Samey thing with audio apps. There was an option to lock the screen and keep an audio themed lock screen wallpaper (turntable/walkman/ipod options were available in stock) on that allowed some finger patterns to work as play/pause, next/previous track.