Recycle to Metal rather than RocketParts.

This makes more sense to me. It will probably mess up some people's bases,
but nothing too serious, I think.
Rework the resource usage logic a bit.

Now even if kethane is not present, EL can be forced to use resources.
Add per-save settings control.

For now, just recourse use forcing, and then only when kethane isn't
present (irrelevant when it is). However, this will make adding all sorts
of persistent info easier :).