>From the metting minutes:

- GeometryType vs. topologyId
  Both shall be merged into GeometryType
    * method id() shall return the topologyId
    * method basicType() shall be extended to return not presentable

Changes:
- GeometryType uses the topologyId internally to represent all types
  covered by topologyId
- an additional flag marks none-state
- new BasicType extended for all topologyId-types not coverd by BasicType
- new method id()

Tested with current dune-grid tests

[[Imported from SVN: r6255]]