Revisit plot titles and axes labels

Inconsistency in language for titles and labels, particularly "streamflow" and "discharge" exist.

Was pointed out in !18 (merged), and the in-place fix has been to revert to language in WaterWatch. We should revisit to make sure the titles and axes labels are what we'd like them to be. Specifically, ensuring that the labels use accepted USGS conventions for units, etc, and the labels are legible. Also that labels are used consistently across the plotting functions.