Update some Swift classes in PlayerPRO Player:
sortMusicListByName: the value types passed to the sort function don't need to be explicitly stated.
Added a sortMusicListUsingComparator command to the music list class.
rename beginLoadingOfMusicListAtURL to beginLoadingOfOldMusicListAtURL.
Change stashedFileSize in MusicListObject from "UInt64" to "UInt64?", that way we don't keep trying to get the size if it fails.
Code style changes.