sub-optimal setup for load-balancing test case

[sradl1981]

hey,

in this example has a sub-optimal setup

https://github.com/ParticulateFlow/LIGGGHTS-PFM/tree/master/examples/LIGGGHTS/PFM/loadbalancing_slow_gran_flow

(STL mesh, missing folders, ...)
this case should fix all issues and make up a better test case:
loadbalancing_slow_gran_flow.zip