skelvp: fog of depth

[Optiligence]

shade nodes in the background (with respect to the current position or active node?) for a better sense of their spacial relation similar to volume vp

[n0void]

This only works well in volume vp since it has uniform depth. 3d vp with its more free camera control is not meant to only focus on what's in the depth's center or front. So I am assuming that adding this feature will likely lead to more problems than solve the issue of proper perception of depth.