v.scatterplot add option to plot lines dividing plot in quandrants

[ecodiv]

• Add an option to plot lines dividing the plot in four quadrants, representing four categories with HH, LL, LH and HL values.
• Changed the parameter n_sd to n (see Standardize parameters addons for plotting (issue #1071 ) #1075)
• Changes parameters xlim and ylim to x_axis_limits and y_axis_limits (see Standardize parameters addons for plotting (issue #1071 ) #1075)
• Changes parameter file_name to output (see Standardize parameters addons for plotting (issue #1071 ) #1075)