Add functions that help a user choose a coarse-graining size

[alexgenin]

This function should print the ic_value ~ coarse_graining size plot so the user can decide on an optimal coarse-graining size.

When the input is several matrices along a gradient, then we don't know on which snapshot this curve should be displayed. Moreover they are not comparable across values of the gradient as density changes.

A rule of thumb could be using (1) something not too close to the tipping point and (2) with a density that is not too high.