Materials should be scoped to the planetoid

[acidboy]

Curious what others think, but I think it would be a huge improvement if a given planetoid had their default element for each machine/building/etc. sticky for that planetoid.  Currently, say, there's a ton of sandstone on one planetoid and a ton of sedimentary rock on another.  It's annoying that despite the fact that one planetoid has a ton of one and the other has a ton of the other -- they both default to whatever is the current element for that building.