Back, use, add, rename, icon, particle count and delete or reset now sit
in the same column of the last row in every particle menu, and columns a
menu does not use show a barrier.
Every menu item now acts on a plain click: slots open their editor with a
use button, entries open their editor, and duplicating is gone. The entry
editor groups settings into labelled rows, numbers and colours get their
own screens instead of relying on right click or Q, and slot names show
the particles per tick used out of the maximum.