Merge branch 'feature/staggered-energy' into 'next'

dumux/discretization/fourierslaw.hh

dumux/discretization/staggered/freeflow/fourierslaw.hh

dumux/freeflow/CMakeLists.txt

dumux/freeflow/staggered/fluxvariables.hh

dumux/freeflow/staggered/localresidual.hh

dumux/freeflow/staggered/model.hh

dumux/freeflow/staggered/properties.hh

dumux/freeflow/staggered/propertydefaults.hh

dumux/freeflow/staggered/volumevariables.hh

dumux/freeflow/staggerednc/fluxvariables.hh

dumux/freeflow/staggerednc/localresidual.hh

dumux/freeflow/staggerednc/model.hh

dumux/freeflow/staggerednc/properties.hh

dumux/freeflow/staggerednc/propertydefaults.hh

dumux/freeflow/staggerednc/volumevariables.hh

dumux/freeflow/staggeredni/CMakeLists.txt

dumux/freeflow/staggeredni/fluxvariables.hh

dumux/freeflow/staggeredni/indices.hh

dumux/freeflow/staggeredni/localresidual.hh

dumux/freeflow/staggeredni/model.hh