Improve output shaded relief figure

[bpurinton]

Also, we should have a big beautiful color shaded relief map in the report. Right now, the only one is small in the 3 col figure with tri error and dh with refDEM. Fine to keep it there, but should also include a full page color hs figure, and perhaps a few smaller panels showing subsets at native DEM resolution w/ image for context. Can systematically extract the subsets from center/corners, or potentially use the tri-error to define windows with min and max error (percentiles? local variance?), and automatically pull and plot those samples. Just want to think about DPI, figsize, DEM posting and subset dimensions.