Updated changelog

git-svn-id: http://openmesh.org/svnrepo/OpenMesh@1024 fdac6126-5c0c-442c-9429-916003d36597
exposed standard property mesh functions (add, remove & availability check)

git-svn-id: http://openmesh.org/svnrepo/OpenMesh@1025 fdac6126-5c0c-442c-9429-916003d36597