Added time-based weighting algorithm

Weights CPIs based on time to accrue the required bits.  Times over ~1h get the highest weights against them to try to further optimize upgrade purchases.

For the curious, the weighting algorithm is:
2<sup>_e_<sup>(time/450)</sup>/4000</sup> - 1

I arrived at it mostly through trial-and-error with a graphing calculator, so it can probably be simplified down.