display physicals by default


git-svn-id: https://geuz.org/svn/gmsh/trunk@16762 59c8cabf-10d6-4a28-b43f-3936b85956c4
document shortcuts


git-svn-id: https://geuz.org/svn/gmsh/trunk@16763 59c8cabf-10d6-4a28-b43f-3936b85956c4