Make the Slow Metabolism Trait depletion rate the new default rate

[awfulworldkid]

new idea: Add another trait that requires Slow Metabolism, and costs 1 instead of being free, but halves depletion rates again on top of the halving from Slow Metabolism. Also add Fast Metabolism, which doubles all depletion rates, and another 1 cost trait that requires Fast Metabolism and doubles them again.