Remove tiles and special_tiles from node definition prototype because otherwise the old names can't be used

Add after_destruct and cache the existence of on_construct, on_destruct and after_destruct for quick skipping when a node does not have them

Shadily clean up NDT_RAILLIKE to surely differ from the few leftover non-LGPLv2 parts from the standpoint of copyright law.

Clean and optimize clouds.cpp enough to not really contain any of the small amount of non-LGPLv2/later code left

Switch the license to be LGPLv2/later, with small parts still remaining as GPLv2/later, by agreement of major contributors