Bugfix: It is wrong to use a shared_ptr for the TimeManager in

OneModelProblem, since the object can be owned by a different class.
This leads to a segfault at the end of test_transport. Therefore, a raw
pointer is taken for the moment. We should carefully rethink this in
general after the release. 
Discussed with Markus.


git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@10278 2fb0f335-1f38-0410-981e-8018bf24f1b0