Rework of the Cumulant-Based Method

doc/notebooks/04_tutorial_cumulant_LBM.ipynb

doc/notebooks/06_tutorial_modifying_method_smagorinsky.ipynb

doc/sphinx/methods.rst

doc/sphinx/moment_transforms.rst

lbmpy/creationfunctions.py

lbmpy/enums.py

lbmpy/forcemodels.py

lbmpy/methods/__init__.py

lbmpy/methods/abstractlbmethod.py

lbmpy/methods/centeredcumulant/__init__.py

lbmpy/methods/centeredcumulant/force_model.py

lbmpy/methods/creationfunctions.py

lbmpy/methods/cumulantbased/__init__.py

lbmpy/methods/cumulantbased/cumulant_simplifications.py

lbmpy/methods/cumulantbased/cumulantbasedmethod.py

lbmpy/methods/cumulantbased/galilean_correction.py

lbmpy/methods/momentbased/centralmomentbasedmethod.py

lbmpy/methods/momentbased/momentbasedsimplifications.py

lbmpy/moment_transforms/__init__.py

lbmpy/moment_transforms/abstractmomenttransform.py