Feature request: Surface Prop's

[JackBekket]

old *.vmt files can have info about material surfaceprop like this:

"$surfaceprop"	"concrete"

which can be write in new *.vmat file like

	SystemAttributes
	{
		PhysicsSurfaceProperties "prop.concrete"
	}

This will allow new material have same surface propierties as original material

It allow to tether soundevents with this material accordingly, meaning that wood will sound like wood, grass as grass, concrete as concrete