[Lua] Rewrite addvfx and spawnvfx

Rewrites animation.addVfx and vfx.spawn to take a model path instead of a static. I don't know what I was smoking making these take a Static.

Moves vfx from core to world. In retrospect this is far more appropriate, especially with an event handler for SpawnVfx making it easy to invoke it from local scripts anyway.

Adds event handlers for AddVfx and SpawnVfx.