Add proper physical material support

[CptNight]

Add Physical materials option for landscape collection per layer

[deanvaessen]

Bumping this ticket. I'm likewise impacted by the absence of this option, which disables quite a few of my systems.

[Phyronnaz]

Instead of storing the section index as material index in the collision data, store an index to an array of phys materials. Use an interface to allow different ways of choosing the phys mat. Maybe refactor hardness to use that too

[Mr4Goosey]

Bumping this because very versatile!

[romesvonwolf]

Wondering if this had been implemented yet

[Phyronnaz]

Not yet, but planned!