Some changes to plotting gridded data!

I am making some changes to how I plot gridded data, which I think will
benefit the viewing experience! Before I was only plotting one field
(e.g., Doppler velocity) at several heights, and this would constitute
one image. Well now I'm plotting four fields per image, and showing each
field every 2 km. This will definitely make it easier to investigate the
data quality, instead of jumping back and forth between images...