Collision object wireframes don't fully render under multi-threaded generation

[Shfty]

Collision wireframes will only partially render after being added to the scene, but can be refreshed by tabbing to a different scene and back.

Likely some sort of property update signal / order of execution bug.

[Shfty]

Fixed by adding children on the main thread at the end of the build process.

This has the unfortunate side-effect of visual geometry no longer rendering in as it's generated, but that's a necessary price to pay for the new (considerably safer and more stable) threading architecture.