[API] Add momentum conservation to the Momentum Exchange Method and hook for PDF destruction
Aidun's method adds the fluid's momentum to the particle when a cell is converted to boundary and transfers momentum from the particle to the fluid when a new fluid cell is uncovered. This pull request provides the option to switch on this momentum conservation.
Also, it adds a hook to the BodyMapping to allow customization of the fluid destruction. This is similar to how the fluid reconstruction is also customizable by a functor.
Finally, it permits applying
PDFReconstruction to ghost layers too, which can be useful if you have fields coupled to your LBM that are restored by a custom reconstructor.