Change doxygen group names from ISTL_Comm to Common_Parallel

dune/common/parallel/communicator.hh

dune/common/parallel/indexset.hh

dune/common/parallel/indicessyncer.hh

dune/common/parallel/interface.hh

dune/common/parallel/localindex.hh

dune/common/parallel/plocalindex.hh

dune/common/parallel/remoteindices.hh

dune/common/parallel/selection.hh