Allow sorting front-to-back

It's currently not possible to render meshes front-to-back.

* it is also be beneficial to skip sorting (fair performance boost) for e.g. alpha blended particles.
See [exploration-particle-no-sort](https://github.com/defold/defold/tree/exploration-particle-no-sort)

* Another useful sort is the y-sort, allowing for objects hiding behind other objects the higher the Y value is.

I think that a material property is the most frequent use case, but I wonder if it's also useful to have it as a render script override as well? We need to find a use case for that before adding it to the render script api.