[Fluxus] 2d overlay + commits

[gabor papp]

> Is there some way image primitives can be integrated with pixel
> primitives? 
i'm not sure how, but we can consider it. image primitive uses its own 
screen space coordinate system and transforms, so state transforms do 
not apply.
if we try to do this, we should merge the fbo-pixels branch to master 
first, because there were a lot of modifications to pixel primitives there.

best,
gabor