Add free-surface LBM extension
This merge request extends waLBerla with a CPU-implementation of the free-surface lattice Boltzmann method as proposed by
Körner C., Thies M., Hofmann T., Thürey N., Rüde U.: Lattice Boltzmann Model for Free Surface Flow for Modeling Foaming.
Journal of Statistical Physics 2005; 121(1): 179–196. doi: 10.1007/s10955-005-8879-8
Edited by Christoph Schwarzmeier