+ Model.checkIfGrabsInput improved by using pixles[] instead of get()
+ Scene.drawModels() and scene.drawModels(pgraphics) to draw models'
contents into an onScreen/offScreen scene resp. Thus allowing shader
chaining as it's shown here:
https://github.com/remixlab/proscene-experiments/tree/master/PostFx. The
approach was similar to that found in scene.post() which draw models'
contents into scene.pickingBuffer