feature : zoom :

- Extracted layers rendering logic from DrawingController to dedicated
  class
- Turned RendererManager into Composite renderer (extends
  AbstractRenderer)
- AbstractRenderer no longer contains a render(frame) method, implementing
  the render differs too much between my current renderers to impose a
  single signature, but I should improve this later if too much time on ma
  hands

js/rendering/AbstractRenderer.js

@@ -3,7 +3,6 @@
 
   ns.AbstractRenderer = function () {};
 
-  ns.AbstractRenderer.prototype.render =         function (frame)  {throw 'abstract method should be implemented';};
   ns.AbstractRenderer.prototype.clear =          function ()       {throw 'abstract method should be implemented';};
 
   ns.AbstractRenderer.prototype.getCoordinates = function (x, y)   {throw 'abstract method should be implemented';};