Conditional lines hide the silhouette edges when the threshold is high

[pailhead]

I did this same thing a while back and used a fall-through of sorts, that you can see here:
https://github.com/pailhead/three-line-outline/blob/master/src/glsl/outline.vert

So the idea if it is an edge that belongs to the outline, just exit early. Otherwise, let the threshold do it's thing, if it's valid, exit again. In the end, move the vertex outside of ndc and dont rasterize.

[gkjohnson]

This sounds good to me - I think right now the dynamic lines and the threshold lines are separate but it would be good to merge them into a common shader. Thanks!