plot1of15: plots 1 of the 15 graphs of streamflow statistics on a single page

Description

Part of the flowHistory system. It is designed to create each of the component graphs for the function plot15. The 15 graphs include annual and four seasonal graphs
for each of 3 flow statistics: 1-day maximum, mean, and 7-day minimum.
The computations involved are the same as the ones used in plotFlowSingle or in makeAnnualSeries