Graph differences in timing tests

[Hubert Kario]

Feature request

Is your feature request related to a problem? Please describe

Currently the conf_interval_plot.png is the only plot that plots differences between samples. That makes it hard to get a "feel" for the shape of distribution and size of noise in the differences.

Describe the solution you'd like

It would be nice to see the ECDF and either the scatter plot or a set of heatmaps for the differences between the first sample and other samples, the way the conf_interval_plot.png does.

Describe alternatives you've considered

while it's not hard to graph them manually using R, they're always useful, and graphing them with R gets tedious

Additional context

issue #673