[cleanup] Consistent spelling of nonwetting/Nonwetting

.../porousmediumflow/nonequilibrium/thermal/localresidual.hh

dumux/porousmediumflow/nonequilibrium/volumevariables.hh

dumux/porousmediumflow/richards/newtonsolver.hh

dumux/porousmediumflow/richards/volumevariables.hh

dumux/porousmediumflow/richardsnc/volumevariables.hh

...multidomain/embedded/1d3d/1p2c_richards2c/problem_soil.hh

test/multidomain/embedded/1d3d/1p_richards/problem_soil.hh

...iumflow/2p2c/implicit/chemicalnonequilibrium/params.input

...low/2p2c/implicit/chemicalnonequilibrium/spatialparams.hh

test/porousmediumflow/mpnc/implicit/kinetic/params.input

test/porousmediumflow/mpnc/implicit/kinetic/spatialparams.hh

.../porousmediumflow/richards/implicit/analytical/problem.hh

test/porousmediumflow/richards/implicit/lens/problem.hh

...low/richards/implicit/nonisothermal/conduction/problem.hh

...low/richards/implicit/nonisothermal/convection/problem.hh

...ow/richards/implicit/nonisothermal/evaporation/problem.hh

test/porousmediumflow/richardsnc/implicit/problem.hh