scatter plot function added to prim

a box now has a scatter plot function analogous to the one found in the
SDtoolkit of Bryant
function for inspecting box in peeling trajectory

convenience function for inspecting an individual box in the peeling
trajectory. It will print the mass, mean, coverage, density, and nr. of
restricted dimensions, as well ass the box limits.
quasi p statistic added to prim

the quasi p statistic is now available. It will be shown when printing
selected boxes from the peeling trajectory using
write_selected_box_to_stdout