rename mods; add `bg_` prefix.
add hacky cleanup ABM (couldn't get LBM:s to work), that converts old
nodes into new ones according to this rename.
the cleanup doesn't do anything for items, though.
move plank registration and recipe out of tree mod into newly created
woodworking mod.
also update plank recipe to require cobblestone instead of stone to be
held while pummeling.
add `log_alive` and `leaves_alive`. make alive logs actually have a top
texture (bottom texture and dead logs are still wrong, though).
slightly refactor some tree growth code.