improvement of handbook:

- removed all (old) occurrences of Dumux 2.1 and Dune 2.1
- updated "Flow of things" to version in the AWR Dumux paper: Included decoupled flow with adaptive gridding.
reviewed by Bernd

git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@9272 2fb0f335-1f38-0410-981e-8018bf24f1b0