fixed more documentation

doc/doxygen/Doxylocal

dumux/boxmodels/1p/1plocalresidual.hh

dumux/boxmodels/2p/2pfluxvariables.hh

dumux/boxmodels/2p2c/2p2clocalresidual.hh

dumux/boxmodels/2p2cni/2p2cnilocalresidual.hh

dumux/boxmodels/2p2cni/2p2cnivolumevariables.hh

dumux/boxmodels/common/boxfvelementgeometry.hh

dumux/boxmodels/common/boxlocaljacobian.hh

dumux/boxmodels/common/boxmodel.hh

dumux/common/math.hh

dumux/material/binarycoefficients/henryiapws.hh

dumux/material/components/component.hh

dumux/material/components/iapws/common.hh