Add an entire function in one mega-commit

This function generates CSV files that contain
completeness percentages per year and per quarter.
It currently takes in the processed NAPS data CSVs.
Add station class factor to data frame

This uses cut to create discrete categories from
continuous population data.
Fix mistake in use of comparison operator
Refine north/south latitude coordinates for Cda
Refine ‘ggmap’ parameters for plotting NAPS stations