Moved rendering functionality in ploma.js to have it available as a plugin

created Ploma module object in ploma.js and moved initialization to init.js. Ploma encapsulates Sketcher prototypes - to create an object that renders stroke arrays, create a Ploma.Sketcher instance with parameters canvas, textureCanvas1 and textureCanvas2. A sketcher instance provides and interface with addPoint, beginStroke and finishStroke and has public values strokes (Array) and curStroke, both the filtered version of points/strokes.
I think this `beginStroke` interface makes sense, thanks!