For drums: Dynamically generates positions maps

[jmmelko]

• [x] Add grid size argument in instrument parser __init__()
• [x] Pass this argument to note parser
• [x] Let note parser calculate position map or better, use a math function
• [x] make Skygrid a class
• [x] Skyjson
• [x] skyabc15
• [x] skykeyboard
• [x] do Rémi
• [x] doremijp
• [x] English
• [x] englishchords
• [x] noteparser