Drawing Engine refactor

[juliandescottes]

The rendering is heavy : need to explicitely call the controller responsible for a given area of the layout, and ask it to redraw its components. And there is no common redraw or render method : for each controller you have to call different methods.

The goal of this task is to make the rendering process automatic.

A drawing loop based on request animation frame will run in the background, and will call the different controllers. The controllers will be responsible for checking the models they are relying upon and will choose the most appropriate way to redraw their UI components.

[juliandescottes]

I consider this as implemented for now.