pummeling definition tables now has lists of item id:s and groups, the
same way e.g. ABM:s do, that determine what items are involved in a
recipe.
update existing (in-use) pummel recipes to make use of this.
clean up things that were broken after renaming `bg_core` to
`bg_terrain`.
also clean up after global rename that added `bg_` prefix to every mod
name.
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.
