Add HUC8-based summaries as some part of regridding QC

[kyleredilla]

We want to make sure that regridding precipitation does not shift precipitation data too much from one basin to another. The downscalers suggested we do the following for validation of precip data regridding: pick some large HUC8s (that can include many 1° grid cells) and summarize within them for both raw and regridded model output, and compare. Also compare visually with HUCs overlaid on top.