New Metric W' Exp

For maximum W' capacity expended i.e. Min W'bal
expressed as a percentage of W'.

So if W' is 20 kJ and W'bal is 2kJ then 18 kJ
have been expended, which when expressed as a
percentage of W' (18/20 %) would be;

Max W' Exp of 90%

I also cleaned up a few extra instances of WPrime
being created when calculatinf metrics which was
not a big deal for the Metric refresh but would make
interval metrics painful.