PROCESSOR: Add discount rate to wood price dialog that applies to Optimizer via its associated Processor scenario

[lbross]

From @jsfried: It would be far less confusing to the user to specify a discount rate for the processor scenario (that carries over also into the optimizer scenario to which it is linked) separate from these escalators. If it is confusing to us (with graduate training in economics) to figure out how to correctly load the different elements we want to account for onto these escalators, it seems a fair assumption that others will also find it daunting.

I think the best bet would be to specify a new, processor scenario variable Discount Rate that gets collected on the wood price dialog and defaults to 0.04 (i.e., 4%). Then let the escalators default to 1, and have the out decade costs and values be adjusted (via multiplication) by both the appropriate escalator and a discount multiplier implied by the assumed 0.04 discount rate, i.e.: