Do not force grids to subclass Entity or Geometry

The current implementation assumes that both the Entity and the Geometry of a grid are subclasses of Dune::Entity and Dune::Geometry. This requirement must have been introduced after 2.4.1 and is IMHO to much of restriction. After all these are just tests. With this MR we drop this additional restriction. Tested with opm-grid.

Closes #36 (closed)

Should be in the release.

Added 2 commits:

• 5d3beb6e - Cleanup: Removed out commented code.
• b50c99c9 - Use GeometryChecker in test-geogrid

Added backport label

Failing build seems unrelated to me.

Mentioned in merge request !117 (merged)

Mentioned in commit 67e5c5a7

Status changed to merged

Mentioned in commit b50e3159

Mentioned in merge request !129 (merged)

Mentioned in commit 0b61d119

Mentioned in commit 2f57a309