Resource density

These are my changes to bring the size of the resource unit in line with the rest of KSP (ie, about 200u per cubic meter), and thus give the ore, metal and rocket parts resources sensible densities. As part of the process, I also tweaked the conversion ratios for ort->metal and metal->rocket parts, but as those files are not in git, here are the relevant lines:

smelter:
    // From http://en.wikipedia.org/wiki/Iron_ore
    // Stage One: 3 Fe2O3 + CO → 2 Fe3O4 + CO2
    // Stage Two: Fe3O4 + CO → 3 FeO + CO2
    // Stage Three: FeO + CO → Fe + CO2
    //
    // Until Kethane supports multiple input/output resources, no point in
    // worrying about CO/CO2.
    //
    // So 3Fe2O3 + 9CO → 6Fe + 9CO2, Fe = 55.845, O = 15.999 which means
    // 479.061g of ore will produce 335.070g of iron. Kethane takes care of the
    // relative densities for us, thus the efficiency is just 355.07/479.061.
    ConversionEfficiency = 0.699431

workshop:
    // There is always some waste when building things (sawing, grinding,
    // cutoffs, etc).
    ConversionEfficiency = 0.9