some Doxygen docu in Common::LocalMatrix
some Doxygen docu in Common::LocalMatrix

git-svn-id: e2a6439806a0c0fcffd1bad863540b8940b422b9@99 4028485c-44d9-4cde-a312-5a4635ee2db9

ftalbrecht/dune-gdt,BarbaraV/dune-gdt