NOTE: QMediaPlayer apparently supports seeking in MP3s now, both in debian and sailfish, so i updated qtcmdplayer to use QMediaPlayer instead of QAudioDecoder for all files, including MP3s (--player-alt can be used to use the old player for old versions of pyqt5-multimedia)

(QMediaPlayer is much more efficient, and unlike QAudioDecoder, doesnt have to decode everything up to a certain point to seek to that point)