new fluid systems: implement the changes discussed last friday

If you have any major objections, speak at meeting on friday or
forever hold your peace.  (Where "forever" means "until the next major
fluid framework refactoring". [Which won't be initiated by me.])

git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@6807 2fb0f335-1f38-0410-981e-8018bf24f1b0