#27 Tech debt

[Csaba Skrabák]

Refactoring:

• musicData.cursor --> var cursor (global, not cloning it)
• musicData.units --> var units = [] (members not jsonified)
• musicData.lily --> function unitsToLily(units)
• musicData.durations: duration field in each unit
• var unit --> units[cursor]
• cloneMusicData --> JSON.stringify/parse