Merge branch 'cleanup/flux-laws' into 'master'

dumux/flux/box/darcyslaw.hh

dumux/flux/box/effectivestresslaw.hh

dumux/flux/box/fickslaw.hh

dumux/flux/box/fourierslaw.hh

dumux/flux/box/fourierslawnonequilibrium.hh

dumux/flux/box/hookeslaw.hh

dumux/flux/box/maxwellstefanslaw.hh

dumux/flux/ccmpfa/fickslaw.hh

dumux/flux/cctpfa/fickslaw.hh

dumux/flux/cctpfa/fourierslaw.hh

dumux/flux/cctpfa/fourierslawnonequilibrium.hh

dumux/flux/cctpfa/maxwellstefanslaw.hh

dumux/flux/shallowwater/riemannproblem.hh

dumux/flux/staggered/freeflow/fickslaw.hh

dumux/flux/staggered/freeflow/maxwellstefanslaw.hh