UAT-217/187/188 Basic heatmap plot esthetic fixes

Color range included (with histogram). Subset legend placed outside of
plot. Labels no longer chopped.
UAT-217/187/188 Improved basic heatmap plot

On the basis of user input, the heatmap size is now completely handled
by the R script (without user input). Size is determined on having
square cells, and guarentees legibility of labels and labels not being
chopped.
Merge branch 'features/plotting_esthetics'