Merge branch 'feature/port-staggered-ff-to-next-next' into 'cleanup/next'

dumux/assembly/staggeredfvassembler.hh

dumux/assembly/staggeredlocalassembler.hh

dumux/common/properties.hh

dumux/common/staggeredfvproblem.hh

dumux/discretization/staggered/connectivitymap.hh

dumux/discretization/staggered/elementfacevariables.hh

dumux/discretization/staggered/elementfluxvariablescache.hh

dumux/discretization/staggered/elementvolumevariables.hh

dumux/discretization/staggered/facesolution.hh

dumux/discretization/staggered/freeflow/facevariables.hh

dumux/discretization/staggered/fvelementgeometry.hh

dumux/discretization/staggered/fvgridgeometry.hh

dumux/discretization/staggered/globalfacevariables.hh

dumux/discretization/staggered/globalfluxvariablescache.hh

dumux/discretization/staggered/globalvolumevariables.hh

dumux/discretization/staggered/properties.hh

dumux/freeflow/properties.hh

dumux/freeflow/staggered/fluxvariables.hh

dumux/freeflow/staggered/fluxvariablescache.hh

dumux/freeflow/staggered/localresidual.hh