Make it an option to not interpolate the Pennsuco Weltands

@bmccloskey I added this option in for EverForecast. Due to the recent 4 gages being dropped from the surfaces, it was no longer able to interpolate PW (because it only uses gages within the EDEN footprint, so the other PW gages aren't included). So I added an option to drop the PW subarea if specified. It should not affect anything in our regular runs but please double check before I break anything. Thanks!

p.s. EverForecast is running off of this branch right now so there's no rush from that perspective on getting this merged.