Merge branch 'AllenCahn' into 'master'

...books/10_tutorial_conservative_allen_cahn_two_phase.ipynb

lbmpy/macroscopic_value_kernels.py

lbmpy/phasefield_allen_cahn/force_model.py

lbmpy/phasefield_allen_cahn/kernel_equations.py

lbmpy/phasefield_allen_cahn/parameter_calculation.py

lbmpy/turbulence_models.py

lbmpy/utils.py

lbmpy_tests/phasefield_allen_cahn/test_analytical.py

lbmpy_tests/phasefield_allen_cahn/test_codegen_3d.py

...hasefield_allen_cahn/test_phase_field_allen_cahn_2d.ipynb

.../phasefield_allen_cahn/test_phase_field_derivatives.ipynb