New items, furniture hit adjustment, itemgroup adjustment

Requires #398

This pr does four things:

Remove the old FurnitureStatic and FurniturePhysics. They are replaced by FurnitureStaticSrv and FurniturePhysicsSrv now.
Add 4 items and 2 furniture (debris themed). They are not implemented yet
Add "use_sprite" property to itemgroups so when they are spawned on the map without a parent furniture, they will assume the sprite they were assigned in the editor. Previously, they would assume a sprite from a random item in their inventory.
Updated the StaticFurnitureSrv hit animation. The problem was that we can't modulate it's color when it uses a shared texture, or all similar furniture will be modulated too. I tried to tween it's position instead, but I think that's not possible when using the RenderingServer. Instead, I have it create a "hit" sprite when it's hit that fades away quickly. We will probably replace this with some SFX down the line

I would add more to this PR but I don't want it to become very big.

Khaligufzel / Dimensionfall