Wrong momentum density calculation for compressible methods with forces.

In conservedquantitycomputation.py (line 210f) the calculation of the momentum density uses the macroscopic velocity shift

mom_density_eq_coll = apply_force_model_shift('macroscopic_velocity_shift', dim, mom_density_eq_coll,
                                              self._forceModel, self._compressible)

which defaults to . When using this momentum density to calculcate the velocity (as it is done in all generated lattice models in waLBerla), we divide by the density again, resulting in the overall velocity equation , which is obviously wrong.

Affected are all lbmpy simulations that work directly on the momentum denisty, and all waLBerla simulations that use generated lattice models and calculate the velocity at some point (in particular, the VTK output will be slightly off).