splitted spatial parameters base file

   - one file (DiscretizationTypeSpatialParametersOneP) includes everything which is valid
     for both, single-phase and multi-phase systems
   - one file (DiscretizationTypeSpatialParameters) includes everything
     which is only valid for multi-phase systems
   - For singel-phase problems this means that the spatial parameters
     class now has to be derived from the ...SpatialParametersOneP base
     class!



git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@6430 2fb0f335-1f38-0410-981e-8018bf24f1b0