change of some interfaces of decoupled 2p model -> now compatible to box

models

   - more general implementation of spatial parameters -> now derived
     from FVSpatialParameters
   - MaterialLaw is now directly set as a Property
   - definition of boundary conditions using BoundaryType
   - problem definition as well as spatial parameters definition now
     compatible to box models



git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@6404 2fb0f335-1f38-0410-981e-8018bf24f1b0