Make circular saw and all cut nodes considered as non-ground content

[SwissalpS]

Let's please consider any cut node not to be ground content. This PR:

• sets circular saw to be non ground content.
• sets all nodes defined from this mod to non ground content, but provides a way to register the few that were considered ground content as such.
• sets all cut nodes (stairs, slabs, etc.) to be treated as non ground content by default, while providing mods to be able to register theirs as ground content if they explicitly want to.

see https://github.com/pandorabox-io/pandorabox.io/issues/836