getDurationTiming() added

Function returns a list of the ON notes with updated duration timing.
Made the function independent from the saveToFile function to allow usage elsewhere.
It does not assign a button to the note

Usage: After MidiParser is initialized

MidiParser mp = new MidiParser(new File("filename.mid"));
List<Note> noteList = mp.getTrackTiming(1).getDurationTiming();

Duration can be accessed with:
Note n = noteList.get(0).getDuration();