Disable particles for building previews

[Kieran P]

When you go to construct a building that contains particles (like the Roman Temple) the particles render properly, but the problem is when you move the building it leaves a trail of smoke, or when you place the building, the smoke remains there even though the foundation doesn't emit anything. It's weird behaviour.

From Philip: "Suggested solution: TemplateManager would add some <DisableParticles/> to VisualActor, VisualActor would then set MODELFLAG_DISABLE_PARTICLES recursively, then particle models would turn themselves off, or something"