Everything can be controlled by the input file: Changing

[Grid]
File = ./grid.dgf

into

[Grid]
File = ./grid.gmsh

or into

[Grid]
LowerLeft = 0 0 0
UpperRight = 1 1 1
Cells = 20 30 10

will construct a gmsh grid or a structured grid instead of the dgf grid.
The grid creator is the new standard grid creator.
To use all features dune 2.4 is required (e.g. structured grid factory)
but it dgf/gmsh works with dune 2.3. The structured grid factories can
be deprecated as soon as dune 2.4 is released.

additional feature:
- set inital refinement in Grid.Refinement  (oder options can be easily
  added, write me)
- grid specific parameter in input file, e.g.  UGGrid: Grid.ClosureType
  = None
turns off green refinement (triangles closure).
- new property GridParameterGroup sets the input file group the grid
  creator is looking in. Particularly useful for two grid simulations:

[DarcyGrid]
File = bla.dgf

[StokesGrid]
File = blub.dgf



git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@15307 2fb0f335-1f38-0410-981e-8018bf24f1b0