Use the Opm::EclipseGrid class instead of the deck directly

this has the advantage that the gazillion ways of specifying an ECL
grid are abstracted away, and thus e.g. using D{X,Y,Z}V is
automatically supported. Also, if additional grid construction methods
are implemented in Opm::EclipseGrid, these will automatically
supported by dune-cornerpoint as well. (If the API for
Opm::EclipseGrid does not change, that is.)
added method subEntities which is a replacement for count. count is still there and just
calls subEntities.
leafView --> leafGridView. Backwards compatibility for dune 2.2 was added.
Merge pull request #98 from robertk-iris/dune-3.0-compat

Dune 3.0 compat
Merge pull request #90 from andlaus/use_EclipseGrid

Use the Opm::EclipseGrid class instead of the deck directly
implement a generic IntersectionMapper class

this class takes an arbitrary dune grid view and makes it possible to
map intersections to a unique, grid-view-global index, where it does
not matter which element is to the interior and which is to the
exterior of the intersection.

For conforming grids, this class provides the same functionality as a
mapper for faces (albeit using a different ordering), but
IntersectionMapper also works for non-conforming grids which only
provide intersections...
add a unit test for the intersection mapper class