Highlight nodes which are on the current plane

[philippotto]

Detailed Description

Highlight nodes which are exactly on the current plane (e.g., in XY viewport highlight the nodes which have z==currentPosition.z) or "gray out" nodes from other planes.

Context

When using a clipping distance larger than the section thickness, nodes from other slices "shine through". Even though this is intended (otherwise, one would tune the clipping distance), it can be hard to see to which slice a node belongs. Usually, I select the node which makes wk jump to its position. Then, I know to which section the node belongs, but this is quite cumbersome.