Target: Fix issues with materials/mirrors/skins/relections/skidmarks/flares misbehaving when user returns to menu and starts another session.

Underlying issue: Simulation is not properly cleaned up when user returns to menu. Heritage of old menu-less versions.

While doing MP fixes for 0.4.7.1 I figured how to fix this for good.

EDIT: Removed due date. Never works out :)