Scene triangles can't be clicked

[ezod]

SceneTriangle objects currently expose the primitive actuals of their OcclusionTriangle members for clicking via Visual mouse pick, but the primitives are extrusions, which cannot be picked.

To resolve this, either support for picking extrusions needs to be added to Visual, or another primitive that can be clicked needs to be used for triangles (which may not exist).

[ezod]

This is still an issue now that SceneTriangle has been removed; objects without primitives have nothing to click on.