Only render dirty part of the scene

[GMartigny]

It could be a huge performance boost to only render part of the scene that need to be redrawn.
The scene could be split into an arbitrary number of parts (3x3 ...) and component should "dirty" the part their into.
Alternatively, component can return informations on their bounding box (AABB). Then scene only redraw the union of all AABB. (see below comment)

[GMartigny]

I implemented a bounding box solution and performances actually got worse. With 1000 component packed in the same area (bounding box relevant) fps drop from ~20 to ~10.

I think, looping through children and computing the box is more expensive than predicted.

[GMartigny]

This issue would be deprecated by #80.