implicit branch: change directory structure. Add dumux/implicit directory. Copy models from boxmodels/model to implicit/model. Copy boxmodels/common to implicit/box. Copy ccmodels/common (from devel) to implicit/cellcentered. Copy boxmodels/common/box*.hh to implicit/common/implicit*.hh. Move test/boxmodels to test/implicit. Adapt configure.ac and Makefile.ams. Everything still builds.

git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/branches/implicit@9679 2fb0f335-1f38-0410-981e-8018bf24f1b0