To all plot files:
  1. removed the source(DataInput.R) command
  2. inserted the code for data input

to plot file 1-2 and 4-6 changed the PNG file sixe to 600 pixels.

To plot6.R:
  1. added code to create a normalized emission for each city
  2. added code to create a plot of the normalized emissions by city using ggplot
  3. added code to create 2 plots in a single PNG file using the gridExtra library and the grid.arrange command.

Removed DataInput.R from git repo
housekeeping