the positions use the scalar specfied by the grid, vectors use the
scalar specified using the property system. a local position has
Grid::dimension entries, a global position has Grid::dimensionsworld entries.

this changes are required to properly support Scalar == quad.

git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@7577 2fb0f335-1f38-0410-981e-8018bf24f1b0