What this MR does / why does DuMux need it: Reduces error messages in doxyerr.log to only two lines:
/temp1/melaniel/dumux1/dumux/dumux/discretization/cellcentered/elementsolution.hh:144: warning: Member documentation for elementSolution found several times in @ingroup groups!
/temp1/melaniel/dumux1/dumux/dumux/discretization/staggered/elementsolution.hh:62: The member will remain in group CCDiscretization, and won't be put into group StaggeredDiscretizationwhich are lines that we already have not been able to get rid of in previous releases.