initial commit for first liggghts coupling

the goal of this branch is to get a working coupling to LIGGGHTS in a
very simple geometry (a sedimenting sphere in a rectangular tank,
maybe a drafting-kissing-tumbling example later)
turns out it works

after quite some struggling with LIGGGHTS and Palabos, the first
coupling works. This is not a nice implementation but a crude "working
hack" that will serve as a basis for further development.
new set spheres algorithm
Example with 140 sedimenting spheres