Merge branch 'freeflow/wallfunctionsForNCNI' into 'master'

doc/handbook/dumux-handbook.bib

dumux/freeflow/navierstokes/problem.hh

dumux/freeflow/navierstokes/staggered/fluxvariables.hh

dumux/freeflow/navierstokes/staggered/localresidual.hh

dumux/freeflow/rans/problem.hh

dumux/freeflow/rans/twoeq/kepsilon/problem.hh

dumux/freeflow/rans/twoeq/kepsilon/volumevariables.hh

dumux/freeflow/rans/twoeq/komega/volumevariables.hh

dumux/freeflow/rans/twoeq/lowrekepsilon/volumevariables.hh

dumux/freeflow/rans/volumevariables.hh

dumux/freeflow/rans/zeroeq/volumevariables.hh

test/freeflow/ransnc/CMakeLists.txt

test/freeflow/ransnc/test_flatplate2cni_wallfunction.input

test/references/test_flatplate_kepsilon2cni.vtu

test/references/test_flatplate_kepsilon2cni_wallfunction.vtu

test/references/test_flatplate_komega2cni.vtu

test/references/test_flatplate_lowrekepsilon2cni.vtu

test/references/test_flatplate_zeroeq2c.vtu

test/references/test_flatplate_zeroeq2cni.vtu