Project 1: plot 4

plot 4: Creates a plot consisting of (4) subplots: (2) previous plots (
plot 2 and plot 3 ) and (2) new X-Y plots that of 'Voltage' and
'Global_reactive_power'
RScript file to create plot 4

plot 4 RScript: script file to load data, reduce data to 2 days of
interest, clean data formats, create quad plot consisting of (4)
subplots and export the plot to a PNG file