introduce new file dumux/common/basicproperties.hh; remove ReferenceElements property from decoupled models; doc

- now every model type tag should be derived from the NumericModel type
tag.
- instead of retrieving the reference elements from the ReferenceElements property,
  use Dune::GenericReferenceElements<Scalar, dim>
- some improvements for the handbook's design patterns and property system chapeters

git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@4626 2fb0f335-1f38-0410-981e-8018bf24f1b0