mark current track implemented
events added,
Prototypes added: setTrackSource, prevTrack, changeVolume
audio event listener added: play, ended, pause, loadedmetadata, timeupdate, durationchange
event listener added: loadedmetadata, timeupdate, durationchange,
event listener added: playactive, stopactive, pauseactive. handle current state of play, pause and stop button
event listener playactive added: displays trackinfos: artist, title, album, genre