Mouse coordinates to cell coordinates, drag and drop handler
Merge branch 'develop0.1' of https://github.com/pogestudio/LetsRuinMusic into develop0.1

Conflicts:
	js/graphics/CellContainer.js
	js/view/CanvasView.js
Merge branch 'develop0.1' of https://github.com/pogestudio/LetsRuinMusic into develop0.1