plot_stackbar function

New function to plot a stacked barplot based on a numeric value (typically EARs). Function allows the user to specify the x and stack factors, and use fill to note the numeric argument to split the colors. User can input color and break points and a facet argument. I created a test function and I think I updated the documentation. But probably would be good to make sure all the files are there. I also used the same mean_logic and sum_logic arguments, and I think they look correct.